Rocky Mountain Oysters<\/h1>\r\n<\/div>\r\nFirst, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.\r\n\r\nTestes and Scrotum<\/h1>\r\n<\/div>\r\nThe two\u00a0[pb_glossary id=\"3486\"]testes[\/pb_glossary]<\/strong> (singular, testis) are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary],<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary].\r\n\r\n[caption id=\"attachment_5159\" align=\"alignnone\" width=\"2048\"]![\"18.3.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Human_reproductive_system_Male-2.jpg\")
Figure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em>[\/caption]\r\nTestes Structure<\/h2>\r\nThe testes are filled with hundreds of tiny tubes, called\u00a0[pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary],<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).\r\n\r\n[caption id=\"attachment_5161\" align=\"aligncenter\" width=\"500\"]![\"18.3.3](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Testicle-2.jpg\")
Figure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em>[\/caption]\r\nTunica<\/h3>\r\nThe multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).\r\n\r\n \t- The\u00a0[pb_glossary id=\"5162\"]tunica vasculosa[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5163\"]tunica albuginea[\/pb_glossary]<\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5164\"]tunica vaginalis[\/pb_glossary]<\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\r\n<\/ul>\r\n
Seminiferous Tubules<\/h3>\r\nOne or more [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called [pb_glossary id=\"5169\"]Sertoli\u00a0cells<\/strong>[\/pb_glossary]. These\u00a0cells\u00a0release a\u00a0hormone\u00a0([pb_glossary id=\"5170\"]inhibin[\/pb_glossary]) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0[pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary]<\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.\r\n\r\n[caption id=\"attachment_5182\" align=\"aligncenter\" width=\"1074\"]![\"18.3.4](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Testis-cross-section-1-2.jpg\")
Figure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em>[\/caption]\r\nOther Scrotal Structures<\/h2>\r\nBesides the two testes, the scrotum also contains a pair of organs called epididymes (singular, [pb_glossary id=\"5090\"]epididymis[\/pb_glossary]) and part of each of the paired [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.\r\nEpididymis<\/h3>\r\nThe [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0[pb_glossary id=\"5090\"]epididymis[\/pb_glossary]<\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.\r\n\r\n[caption id=\"attachment_5173\" align=\"aligncenter\" width=\"453\"]![\"18.3.5](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Epididymis-KDS-2.jpg\")
Figure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em>[\/caption]\r\nVas Deferens<\/em><\/h3>\r\nThe\u00a0[pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary],<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], and continue up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. They are composed of ciliated epithelium and [pb_glossary id=\"2982\"]smooth muscle[\/pb_glossary]. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>, which are accessory structures of the male reproductive system.<\/span>\r\n\r\nAccessory Structures<\/h1>\r\n<\/div>\r\nIn addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.\r\n\r\n[caption id=\"attachment_5175\" align=\"alignnone\" width=\"1024\"]![\"18.3.6](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/3D_Medical_Animation_Vas_Deferens-1-2.jpg\")
Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em>[\/caption]\r\nSeminal Vesicles<\/h2>\r\nThe\u00a0[pb_glossary id=\"5097\"]seminal vesicle<\/strong>s<\/strong>[\/pb_glossary]<\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>[pb_glossary id=\"4885\"]semen[\/pb_glossary],<\/strong>\u00a0which is the sperm-containing fluid that leaves the [pb_glossary id=\"5091\"]penis[\/pb_glossary] during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary]. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0[pb_glossary id=\"4330\"]pH[\/pb_glossary]\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female [pb_glossary id=\"5143\"]vagina[\/pb_glossary]. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span>\r\nEjaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"]![\"18.3.7](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Penile-Clitoral_Structure-2.png\")
Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"]![\"18.3.8](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Penis_cross_section.svg_-2.png\")
Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n![\"\"](\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/logo_ck12.png\")
\u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span>![\"CK-12](\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/icon_licence.png\" "\\"CK-12")
<\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\n![\"18.3.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Lamb_fries-2.jpg\")
Figure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Testes and Scrotum<\/h1>\r\n<\/div>\r\nThe two\u00a0[pb_glossary id=\"3486\"]testes[\/pb_glossary]<\/strong> (singular, testis) are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary],<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary].\r\n\r\n[caption id=\"attachment_5159\" align=\"alignnone\" width=\"2048\"] Figure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em>[\/caption]\r\nTestes Structure<\/h2>\r\nThe testes are filled with hundreds of tiny tubes, called\u00a0[pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary],<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).\r\n\r\n[caption id=\"attachment_5161\" align=\"aligncenter\" width=\"500\"] Figure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em>[\/caption]\r\nTunica<\/h3>\r\nThe multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).\r\n\r\n \t- The\u00a0[pb_glossary id=\"5162\"]tunica vasculosa[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5163\"]tunica albuginea[\/pb_glossary]<\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5164\"]tunica vaginalis[\/pb_glossary]<\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\r\n<\/ul>\r\n
Seminiferous Tubules<\/h3>\r\nOne or more [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called [pb_glossary id=\"5169\"]Sertoli\u00a0cells<\/strong>[\/pb_glossary]. These\u00a0cells\u00a0release a\u00a0hormone\u00a0([pb_glossary id=\"5170\"]inhibin[\/pb_glossary]) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0[pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary]<\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.\r\n\r\n[caption id=\"attachment_5182\" align=\"aligncenter\" width=\"1074\"] Figure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em>[\/caption]\r\nOther Scrotal Structures<\/h2>\r\nBesides the two testes, the scrotum also contains a pair of organs called epididymes (singular, [pb_glossary id=\"5090\"]epididymis[\/pb_glossary]) and part of each of the paired [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.\r\nEpididymis<\/h3>\r\nThe [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0[pb_glossary id=\"5090\"]epididymis[\/pb_glossary]<\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.\r\n\r\n[caption id=\"attachment_5173\" align=\"aligncenter\" width=\"453\"] Figure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em>[\/caption]\r\nVas Deferens<\/em><\/h3>\r\nThe\u00a0[pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary],<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], and continue up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. They are composed of ciliated epithelium and [pb_glossary id=\"2982\"]smooth muscle[\/pb_glossary]. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>, which are accessory structures of the male reproductive system.<\/span>\r\n\r\nAccessory Structures<\/h1>\r\n<\/div>\r\nIn addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.\r\n\r\n[caption id=\"attachment_5175\" align=\"alignnone\" width=\"1024\"] Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em>[\/caption]\r\nSeminal Vesicles<\/h2>\r\nThe\u00a0[pb_glossary id=\"5097\"]seminal vesicle<\/strong>s<\/strong>[\/pb_glossary]<\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>[pb_glossary id=\"4885\"]semen[\/pb_glossary],<\/strong>\u00a0which is the sperm-containing fluid that leaves the [pb_glossary id=\"5091\"]penis[\/pb_glossary] during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary]. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0[pb_glossary id=\"4330\"]pH[\/pb_glossary]\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female [pb_glossary id=\"5143\"]vagina[\/pb_glossary]. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span>\r\nEjaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Figure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em>[\/caption]\r\nTunica<\/h3>\r\nThe multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).\r\n\r\n \t- The\u00a0[pb_glossary id=\"5162\"]tunica vasculosa[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5163\"]tunica albuginea[\/pb_glossary]<\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5164\"]tunica vaginalis[\/pb_glossary]<\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\r\n<\/ul>\r\n
Seminiferous Tubules<\/h3>\r\nOne or more [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called [pb_glossary id=\"5169\"]Sertoli\u00a0cells<\/strong>[\/pb_glossary]. These\u00a0cells\u00a0release a\u00a0hormone\u00a0([pb_glossary id=\"5170\"]inhibin[\/pb_glossary]) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0[pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary]<\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.\r\n\r\n[caption id=\"attachment_5182\" align=\"aligncenter\" width=\"1074\"] Figure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em>[\/caption]\r\nOther Scrotal Structures<\/h2>\r\nBesides the two testes, the scrotum also contains a pair of organs called epididymes (singular, [pb_glossary id=\"5090\"]epididymis[\/pb_glossary]) and part of each of the paired [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.\r\nEpididymis<\/h3>\r\nThe [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0[pb_glossary id=\"5090\"]epididymis[\/pb_glossary]<\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.\r\n\r\n[caption id=\"attachment_5173\" align=\"aligncenter\" width=\"453\"] Figure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em>[\/caption]\r\nVas Deferens<\/em><\/h3>\r\nThe\u00a0[pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary],<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], and continue up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. They are composed of ciliated epithelium and [pb_glossary id=\"2982\"]smooth muscle[\/pb_glossary]. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>, which are accessory structures of the male reproductive system.<\/span>\r\n\r\nAccessory Structures<\/h1>\r\n<\/div>\r\nIn addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.\r\n\r\n[caption id=\"attachment_5175\" align=\"alignnone\" width=\"1024\"] Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em>[\/caption]\r\nSeminal Vesicles<\/h2>\r\nThe\u00a0[pb_glossary id=\"5097\"]seminal vesicle<\/strong>s<\/strong>[\/pb_glossary]<\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>[pb_glossary id=\"4885\"]semen[\/pb_glossary],<\/strong>\u00a0which is the sperm-containing fluid that leaves the [pb_glossary id=\"5091\"]penis[\/pb_glossary] during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary]. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0[pb_glossary id=\"4330\"]pH[\/pb_glossary]\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female [pb_glossary id=\"5143\"]vagina[\/pb_glossary]. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span>\r\nEjaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Seminiferous Tubules<\/h3>\r\nOne or more [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called [pb_glossary id=\"5169\"]Sertoli\u00a0cells<\/strong>[\/pb_glossary]. These\u00a0cells\u00a0release a\u00a0hormone\u00a0([pb_glossary id=\"5170\"]inhibin[\/pb_glossary]) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0[pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary]<\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.\r\n\r\n[caption id=\"attachment_5182\" align=\"aligncenter\" width=\"1074\"] Figure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em>[\/caption]\r\nOther Scrotal Structures<\/h2>\r\nBesides the two testes, the scrotum also contains a pair of organs called epididymes (singular, [pb_glossary id=\"5090\"]epididymis[\/pb_glossary]) and part of each of the paired [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.\r\nEpididymis<\/h3>\r\nThe [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0[pb_glossary id=\"5090\"]epididymis[\/pb_glossary]<\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.\r\n\r\n[caption id=\"attachment_5173\" align=\"aligncenter\" width=\"453\"] Figure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em>[\/caption]\r\nVas Deferens<\/em><\/h3>\r\nThe\u00a0[pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary],<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], and continue up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. They are composed of ciliated epithelium and [pb_glossary id=\"2982\"]smooth muscle[\/pb_glossary]. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>, which are accessory structures of the male reproductive system.<\/span>\r\n\r\nAccessory Structures<\/h1>\r\n<\/div>\r\nIn addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.\r\n\r\n[caption id=\"attachment_5175\" align=\"alignnone\" width=\"1024\"] Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em>[\/caption]\r\nSeminal Vesicles<\/h2>\r\nThe\u00a0[pb_glossary id=\"5097\"]seminal vesicle<\/strong>s<\/strong>[\/pb_glossary]<\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>[pb_glossary id=\"4885\"]semen[\/pb_glossary],<\/strong>\u00a0which is the sperm-containing fluid that leaves the [pb_glossary id=\"5091\"]penis[\/pb_glossary] during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary]. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0[pb_glossary id=\"4330\"]pH[\/pb_glossary]\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female [pb_glossary id=\"5143\"]vagina[\/pb_glossary]. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span>\r\nEjaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Epididymis<\/h3>\r\nThe [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary] within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0[pb_glossary id=\"5090\"]epididymis[\/pb_glossary]<\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.\r\n\r\n[caption id=\"attachment_5173\" align=\"aligncenter\" width=\"453\"] Figure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em>[\/caption]\r\nVas Deferens<\/em><\/h3>\r\nThe\u00a0[pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary],<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], and continue up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. They are composed of ciliated epithelium and [pb_glossary id=\"2982\"]smooth muscle[\/pb_glossary]. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>, which are accessory structures of the male reproductive system.<\/span>\r\n\r\nAccessory Structures<\/h1>\r\n<\/div>\r\nIn addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.\r\n\r\n[caption id=\"attachment_5175\" align=\"alignnone\" width=\"1024\"] Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em>[\/caption]\r\nSeminal Vesicles<\/h2>\r\nThe\u00a0[pb_glossary id=\"5097\"]seminal vesicle<\/strong>s<\/strong>[\/pb_glossary]<\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>[pb_glossary id=\"4885\"]semen[\/pb_glossary],<\/strong>\u00a0which is the sperm-containing fluid that leaves the [pb_glossary id=\"5091\"]penis[\/pb_glossary] during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary]. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0[pb_glossary id=\"4330\"]pH[\/pb_glossary]\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female [pb_glossary id=\"5143\"]vagina[\/pb_glossary]. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span>\r\nEjaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Accessory Structures<\/h1>\r\n<\/div>\r\nIn addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.\r\n\r\n[caption id=\"attachment_5175\" align=\"alignnone\" width=\"1024\"] Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em>[\/caption]\r\nSeminal Vesicles<\/h2>\r\nThe\u00a0[pb_glossary id=\"5097\"]seminal vesicle<\/strong>s<\/strong>[\/pb_glossary]<\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>[pb_glossary id=\"4885\"]semen[\/pb_glossary],<\/strong>\u00a0which is the sperm-containing fluid that leaves the [pb_glossary id=\"5091\"]penis[\/pb_glossary] during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary]. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0[pb_glossary id=\"4330\"]pH[\/pb_glossary]\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female [pb_glossary id=\"5143\"]vagina[\/pb_glossary]. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span>\r\nEjaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Ejaculatory Ducts<\/h2>\r\nThe\u00a0[pb_glossary id=\"5174\"]ejaculatory duct<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span>\r\nProstate Gland<\/h2>\r\nThe\u00a0[pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]<\/strong> is located just below the seminal vesicles. It is a walnut-sized organ that surrounds the urethra and its junction with the two ejaculatory ducts. The function of the prostate gland is to secrete a slightly alkaline fluid that constitutes close to 30% of the total volume of semen. Prostate fluid contains small quantities of\u00a0proteins, such as\u00a0enzymes. In addition, it has a very high\u00a0concentration\u00a0of zinc, which is an important nutrient for maintaining sperm quality and motility.\r\nBulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Bulbourethral Glands<\/h2>\r\nAlso called Cowper\u2019s glands, the two\u00a0[pb_glossary id=\"5183\"]bulbourethral gland<\/strong>s<\/strong>[\/pb_glossary]<\/strong>\u00a0are each about the size of a pea and located just below the prostate gland. The bulbourethral glands secrete a clear, alkaline fluid that is rich in\u00a0proteins. Each of the glands has a short duct that carries the secretions into the urethra, where they make up a tiny percentage of the total volume of semen. The function of the bulbourethral secretions is to help lubricate the urethra and neutralize any urine (which is acidic) that may remain in the urethra.<\/span>\r\n\r\n[h5p id=\"644\"]\r\n\r\nFigure 18.3.7 Male reproductive system.<\/em>\r\n\r\nPenis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Penis<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5091\"]penis[\/pb_glossary]<\/strong>\u00a0is the external male organ that has the reproductive function of delivering sperm to the female reproductive tract. This function is called intromission. The penis also serves as the organ that excretes urine.\r\nStructure of the Penis<\/h2>\r\nThe structure of the penis and its location relative to other reproductive organs are shown in Figure 18.3.8. The part of the penis that is located inside the body and out of sight is called the root of the penis. The shaft of the penis is the part of the penis that is outside the body. The enlarged, bulbous end of the shaft is called the glans penis.\r\n\r\n[caption id=\"attachment_5184\" align=\"aligncenter\" width=\"297\"] Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Figure 18.3.8 This cross section shows the internal anatomy of the penis and related structures. The corpus spongiosum is the column of erectile tissue that contains the urethra. It is sometimes referred to simply as corpus cavernosum, like the other two columns of spongy tissue in the penis.<\/em>[\/caption]\r\nUrethra<\/h2>\r\nThe [pb_glossary id=\"4732\"]urethra[\/pb_glossary] passes through the penis to carry urine from the bladder \u2014 or [pb_glossary id=\"4885\"]semen[\/pb_glossary] from the ejaculatory ducts \u2014 through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary], where the urethra is joined by the [pb_glossary id=\"5174\"]ejaculatory ducts<\/span>[\/pb_glossary]<\/span>. From there, the urethra passes through the [pb_glossary id=\"5091\"]penis[\/pb_glossary] to its external opening at the tip of the glans penis. Called the external urethral orifice, this opening provides a way for urine or semen to leave the body.<\/span>\r\nTissues of the Penis<\/h2>\r\nThe penis is covered with skin (epithelium) that is unattached and free to move over the body of the penis. In an uncircumcised male, the glans penis is also mainly covered by epithelium, which (in this location) is called the [pb_glossary id=\"5186\"]foreskin[\/pb_glossary], and below which is a layer of [pb_glossary id=\"3538\"]mucous membrane[\/pb_glossary]. The foreskin is attached to the penis at an area on the underside of the penis called the [pb_glossary id=\"5187\"]frenulum[\/pb_glossary].\r\n\r\nAs shown in the Figure 18.3.9, the interior of the penis consists of three columns of spongy tissue that can fill with blood and swell in size, allowing the penis to become erect. This spongy tissue is called [pb_glossary id=\"5188\"]corpus cavernosum[\/pb_glossary] (plural, corpora cavernosa). Two columns of this tissue run side by side along the top of the shaft, and one column runs along the bottom of the shaft. The [pb_glossary id=\"4732\"]urethra[\/pb_glossary] runs through this bottom column of spongy tissue, which is sometimes called [pb_glossary id=\"5189\"]corpus spongiosum[\/pb_glossary]. The [pb_glossary id=\"5190\"]glans penis[\/pb_glossary] also consists mostly of spongy erectile tissue. [pb_glossary id=\"4386\"]Veins<\/span>[\/pb_glossary]<\/span>\u00a0and [pb_glossary id=\"4385\"]arteries[\/pb_glossary] run along the top of the penis, allowing blood circulation through the spongy tissues.<\/span>\r\n\r\n[caption id=\"attachment_5185\" align=\"aligncenter\" width=\"571\"] Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
Figure 18.3.9 The penis consists mostly of spongy tissues that can fill with blood, stiffening the organ. The corpus cavernosum urethrae is now usually called corpus spongiosum.<\/em>[\/caption]\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nLung,\u00a0heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation\u2019s first penis transplant took place, it was considered very newsworthy.\r\n\r\nIn 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. Within 6 months, the patient was able to urinate properly and was beginning to regain sexual function.\u00a0 The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.\r\n\r\nThe 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world\u2019s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.\r\n\r\nIn 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.\r\n\r\n\r\n18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
18.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- \r\n
\r\n \t- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\nAsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\nGallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n\nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\nFigure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\nTestes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\nFigure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\nTunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
\n- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\nFigure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\nOther Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\nEpididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\nFigure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\nVas Deferens<\/em><\/h3>\nThe\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\nFigure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\nSeminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\nEjaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\nProstate Gland<\/h2>\n
- \r\n \t
- The two [pb_glossary id=\"3486\"]testes[\/pb_glossary] are [pb_glossary id=\"2506\"]sperm[\/pb_glossary]- and [pb_glossary id=\"3409\"]testosterone[\/pb_glossary]-producing male [pb_glossary id=\"3408\"]gonads[\/pb_glossary]. They are contained within the [pb_glossary id=\"5089\"]scrotum[\/pb_glossary], a pouch that hangs down behind the [pb_glossary id=\"5091\"]penis[\/pb_glossary]. The testes are filled with hundreds of tiny, tightly coiled [pb_glossary id=\"5160\"]seminiferous tubules[\/pb_glossary], where sperm are produced. The tubules contain sperm in different stages of\u00a0development\u00a0and also [pb_glossary id=\"5169\"]Sertoli cells[\/pb_glossary], which secrete substances needed for sperm production. Between the tubules are [pb_glossary id=\"5171\"]Leydig cells[\/pb_glossary], which secrete testosterone.<\/li>\r\n \t
- Also contained within the scrotum are the two epididymes. Each [pb_glossary id=\"5090\"]epididymis[\/pb_glossary] is a tightly coiled tubule where sperm mature and are stored until they leave the body during an [pb_glossary id=\"5150\"]ejaculation[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5095\"]vas deferens<\/em>[\/pb_glossary] are long, thin tubes that run from the scrotum up into the [pb_glossary id=\"2992\"]pelvic cavity[\/pb_glossary]. During ejaculation, each vas deferens<\/em> carries sperm from one of the two epididymes to one of the pair of [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary].<\/li>\r\n \t
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
- The paired [pb_glossary id=\"5174\"]ejaculatory ducts[\/pb_glossary]\u00a0form where the vas deferens<\/em> joins with the ducts of the seminal vesicles in the [pb_glossary id=\"5096\"]prostate gland[\/pb_glossary]. They connect the vas deferens<\/em> with the [pb_glossary id=\"4732\"]urethra[\/pb_glossary]. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen.<\/li>\r\n \t
- The prostate gland is located just below the seminal vesicles, and it surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.<\/li>\r\n \t
- The paired [pb_glossary id=\"5183\"]bulbourethral glands[\/pb_glossary]\u00a0are located just below the prostate gland. They secrete a tiny amount\u00a0of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic [pb_glossary id=\"4717\"]urine[\/pb_glossary] it may contain.<\/li>\r\n \t
- The penis is the external male organ that has the reproductive function of intromission, which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for [pb_glossary id=\"5149\"]sexual intercourse[\/pb_glossary] so intromission\u00a0can\u00a0occur.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 18.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- \r\n
- \r\n \t
- [h5p id=\"645\"]<\/li>\r\n \t
- Describe the structure of a testis.<\/li>\r\n \t
- Which parts of the\u00a0male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?<\/li>\r\n \t
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens<\/em> so that sperm cannot be ejaculated out of the body. Do you think men who have a vasectomy emit semen when they ejaculate? Why or why not?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 18.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/youtu.be\/k60M1h-DKVY\r\nHuman Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.<\/p>\r\nhttps:\/\/youtu.be\/D1et5NgT6bQ\r\n
The Science of 'Morning Wood', AsapSCIENCE, 2012.<\/p>\r\nhttps:\/\/youtu.be\/Ot7CYjm9B7U\r\n
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 18.3.1<\/strong>\r\n\r\nLamb_fries<\/a> by Paul Lowry<\/a> on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n\r\n\r\nFigure 18.3.2<\/strong>\r\n\r\nHuman_reproductive_system_(Male)<\/a> by Baresh25<\/a> on Wikimedia Commons is used under a\u00a0CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 18.3.3<\/strong>\r\n\r\nTesticle<\/a> by Unknown Illustrator from National Cancer Institute<\/a>, of the National Institutes of Health<\/a>, Visuals Online, ID 1769<\/a> i<\/a>s in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 18.3.4<\/strong>\r\n\r\nTestis-cross-section<\/a> by Laura Guerin from CK-12 Foundation<\/a> is used under a\u00a0<\/span>\r\n<\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n
\u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 18.3.5<\/strong>\r\n\r\nEpididymis-KDS<\/a> by KDS444<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0) license.\r\n\r\nFigure 18.3.6<\/strong>\r\n\r\n3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by https:\/\/www.scientificanimations.com\/wiki-images<\/a> (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 18.3.7<\/strong>\r\nMale anatomy blank<\/a> [adapted] by Tsaitgaist<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Original: <\/span>Male anatomy.png)<\/a><\/p>\r\nFigure 18.3.8<\/strong>\r\n\r\nPenile-Clitoral_Structure<\/a> by Esseh<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 18.3.9<\/strong>\r\n\r\nPenis_cross_section.svg<\/a> by Mcstrother<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\n\r\nReferences<\/span>\r\n
AsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https:\/\/www.youtube.com\/watch?v=D1et5NgT6bQ&feature=youtu.be<\/p>\r\n
Associated Press. (2016, May 17). Man receives new penis in 15-hour operation, the first transplant of its kind in U.S. history [online article]. Canada.com. http:\/\/www.canada.com\/health\/receives+penis+hour+operation+first+transplant+kind+history\/11922832\/story.html<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology<\/em> (Section 25.1) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-biology\/section\/25.1\/<\/p>\r\n
Gallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https:\/\/www.bbc.com\/news\/health-31876219<\/p>\r\n
Grady, D. (2016, May 16).\u00a0 Cancer survivor receives first penis transplant in the United States [online article]. New York Times. https:\/\/www.nytimes.com\/2016\/05\/17\/health\/thomas-manning-first-penis-transplant-in-us.html<\/p>\r\n
Janux. (2015, August 16). Human physiology - Functional anatomy of the male reproductive system (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=k60M1h-DKVY&feature=youtu.be<\/p>\r\n
This Morning. (2016, June 15). I had one of the world's first penis transplants - Thomas Manning | This Morning. YouTube. https:\/\/www.youtube.com\/watch?v=Ot7CYjm9B7U&feature=youtu.be<\/p>","rendered":"
<\/p>\n
Figure 18.3.1 Those are some odd looking oysters…<\/em><\/figcaption><\/figure>\n \nRocky Mountain Oysters<\/h1>\n<\/div>\n
First, they are peeled and pounded flat. Then, they are coated in flour, seasoned with salt and pepper, and deep fried. What are they? They are often called Rocky Mountain oysters, but they don\u2019t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef \u2014 all names that hint at their origins. Here\u2019s another hint: they are harvested only from male\u00a0animals, such as bulls or sheep. What are they? In a word: testes.<\/p>\n
\nTestes and Scrotum<\/h1>\n<\/div>\n
The two\u00a0testes<\/a><\/strong> (singular, testis) are sperm<\/a>– and testosterone<\/a>-producing gonads in male mammals, including male humans. These and other organs of the human male reproductive system are shown in Figure 18.3.2. The testes are contained within the scrotum<\/a>,<\/strong>\u00a0a pouch made of skin and smooth muscle that hangs down behind the penis<\/a>.<\/p>\n
Figure 18.3.2 The male reproductive system includes external organs (such as the penis and testes), and internal organs (such as the prostate gland and seminal vesicles). This view shows the organs from the side, so only one of each paired organ (such as the testes and seminal vesicles) is pictured.<\/em><\/figcaption><\/figure>\n Testes Structure<\/h2>\n
The testes are filled with hundreds of tiny tubes, called\u00a0seminiferous tubules<\/a>,<\/strong> which are the functional units of the testes. As shown in the longitudinal-section drawing of a testis in Figure 18.3.3, the seminiferous tubules are coiled and tightly packed within divisions of the testis called lobules. Lobules are separated from one another by internal walls (or septa).<\/p>\n
Figure 18.3.3 This longitudinal-section drawing includes a testis on the left, its corresponding epididymis in the centre, and its related vas (or ductus) deferens on the right. The three structures are connected to create a tract through which sperm can travel.<\/em><\/figcaption><\/figure>\n Tunica<\/h3>\n
The multi-layered covering of each testis, called the tunica, protects the organ, ensures its blood supply, and separates the testis into lobules. There are three layers of the tunica: the tunica vasculosa, tunica albuginea, and tunica vaginalis. The latter two layers are labeled in the drawing above (Figure 18.3.3).<\/p>\n
- \n
- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vaginalis<\/a><\/strong>\u00a0is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces\u00a0friction\u00a0between the testes and the scrotum.<\/li>\n<\/ul>\n
Seminiferous Tubules<\/h3>\n
One or more seminiferous tubules<\/a> are tightly coiled within each of the hundreds of lobules in the testis. A single testis normally contains a total of about 30 metres of these tightly packed tubules! As shown in the cross-sectional drawing of a seminiferous tubule in Figure 18.3.4, the tubule contains sperm in several different stages of development (spermatogonia, spermatocytes, spermatids, and spermatozoa). The seminiferous tubule is also lined with epithelial cells called Sertoli\u00a0cells<\/strong><\/a>. These\u00a0cells\u00a0release a\u00a0hormone\u00a0(inhibin<\/a>) that helps regulate\u00a0sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the\u00a0blood\u00a0into the tubules. This prevents the male\u2019s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called\u00a0Leydig cells<\/a><\/strong>, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.<\/p>\n
Figure 18.3.4 A cross-sectional drawing of a testis and seminiferous tubule shows the lining of Sertoli cells and sperm in different stages of development within the tubule, and Leydig cells surrounding the tubule.<\/em><\/figcaption><\/figure>\n Other Scrotal Structures<\/h2>\n
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis<\/a>) and part of each of the paired vas deferens<\/em><\/a> (or ducti deferens). Both structures play important functions in the production or transport of\u00a0sperm.<\/p>\n
Epididymis<\/h3>\n
The seminiferous tubules<\/a> within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each\u00a0epididymis<\/a><\/strong> (plural, epididymes) consists of a tightly coiled tubule with a total length of about 6 metres. As shown in Figure 18.3.5, the epididymis is generally divided into three parts: the head (which rests on top of the testis), the body (which drapes down the side of the testis), and the tail (which joins with the vas deferens<\/em> near the bottom of the testis). The functions of the two epididymes are to mature sperm, and then to store that mature sperm until they leave the body during an ejaculation, when they pass the sperm on to the vas deferens<\/em>.<\/p>\n
Figure 18.3.5 Each epididymis consists of a (a) head, (b) body, and (c) tail. The latter is directly connected to the (d) <\/em>vas deferens. The gray egg-shaped structure in the drawing is the testis.<\/em><\/figcaption><\/figure>\n Vas Deferens<\/em><\/h3>\n
The\u00a0vas deferens<\/em><\/a>,<\/strong> also known as sperm ducts, are a pair of thin tubes, each about 30 cm (almost 12 in) long, which begin at the epididymes in the scrotum<\/a>, and continue up into the pelvic cavity<\/a>. They are composed of ciliated epithelium and smooth muscle<\/a>. These structures help the vas deferens<\/em> fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts<\/span><\/a><\/span>, which are accessory structures of the male reproductive system.<\/span><\/p>\n
\nAccessory Structures<\/h1>\n<\/div>\n
In addition to the structures within the scrotum, the male reproductive system includes several internal accessory structures that are shown in the detailed drawing in Figure 18.3.6. They include the ejaculatory ducts, seminal vesicles, and the prostate and bulbourethral (Cowper\u2019s) glands.<\/p>\n
Figure 18.3.6 This detailed cross-sectional drawing of the male reproductive system clearly shows the accessory organs of reproduction, including the seminal vesicles, prostate gland, and Cowper\u2019s (bulbourethral) glands. Secretions from these structures help to form semen.<\/em><\/figcaption><\/figure>\n Seminal Vesicles<\/h2>\n
The\u00a0seminal vesicle<\/strong>s<\/strong><\/a><\/strong> are a pair of exocrine glands that each consist of a single tube, which is folded and coiled upon itself. Each vesicle is about 5 cm (almost 2 in) long and has an excretory duct that merges with the vas deferens<\/em><\/a> to form one of the two ejaculatory ducts. Fluid secreted by the seminal vesicles into the ducts makes up about 70% of the total volume of <\/span>semen<\/a>,<\/strong>\u00a0which is the sperm-containing fluid that leaves the penis<\/a> during an ejaculation<\/a>. The fluid from the seminal vesicles is alkaline, so it gives semen a basic\u00a0pH<\/a>\u00a0that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina<\/a>. Fluid from the seminal vesicles also contains\u00a0proteins, fructose (a simple sugar), and other substances that help nourish sperm.<\/span><\/p>\n
Ejaculatory Ducts<\/h2>\n
The\u00a0ejaculatory duct<\/strong>s<\/strong><\/a><\/strong>\u00a0form where the vas deferens<\/em> join with the ducts of the seminal vesicles in the prostate gland<\/a>. They connect the vas deferens<\/em> with the urethra<\/a>. The ejaculatory ducts carry sperm from the vas deferens<\/em>, as well as secretions from the seminal vesicles and prostate gland that together form semen. The substances secreted into semen by the glands as it passes through the ejaculatory ducts control its\u00a0pH\u00a0and provide\u00a0nutrients\u00a0to sperm, among other functions. The fluid itself provides sperm with a medium in which to \u201cswim.\u201d<\/span><\/p>\n
Prostate Gland<\/h2>\n
- The\u00a0tunica albuginea<\/a><\/strong>\u00a0is the middle layer of the tunica. It is a dense layer of fibrous tissue that encases the testis. It also extends into the testis, creating the septa between lobules.<\/li>\n
- The\u00a0tunica vasculosa<\/a><\/strong>\u00a0is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry\u00a0blood\u00a0to and from the testis.<\/li>\n
- The two [pb_glossary id=\"5097\"]seminal vesicles[\/pb_glossary] are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens<\/em> and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. [pb_glossary id=\"4885\"]Semen[\/pb_glossary] contains alkaline substances and\u00a0nutrients\u00a0that sperm need to survive and \u201cswim\u201d in the female reproductive tract.<\/li>\r\n \t
![Lamb_fries<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Lamb_fries.jpg\"){kind=link}
![Human_reproductive_system_(Male)<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Human_reproductive_system_(Male).jpg\"){kind=link}
![Testicle<\/a> by Unknown Illustrator from](\"https:\/\/commons.wikimedia.org\/wiki\/File:Testicle.jpg\"){kind=link}
![Epididymis-KDS<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Epididymis-KDS.jpg\"){kind=link}
![3D_Medical_Animation_Vas_Deferens<\/a>\u00a0by](\"https:\/\/commons.wikimedia.org\/wiki\/File:3D_Medical_Animation_Vas_Deferens.jpg\"){kind=link}
![Male anatomy blank<\/a> [adapted] by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Male_anatomy_blank.svg\"){kind=link}
![Penile-Clitoral_Structure<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Penile-Clitoral_Structure.JPG\"){kind=link}
![Penis_cross_section.svg<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Penis_cross_section.svg\"){kind=link}