18.9 Disorders of the Female Reproductive System
Vaccinating Against Cancer
Can a vaccine prevent cancer? In the case of cervical cancer, it can. Cervical cancer is one of three disorders of the female reproductive system described in detail in this concept. Of the three, only cervical cancer can be prevented with a vaccine.
Cervical Cancer
Cervical cancer occurs when cells of the cervix (neck of the uterus) grow abnormally and develop the ability to invade nearby tissues or spread to other parts of the body, such as the abdomen or lungs. Figure 18.9.2 shows the location of the cervix and the appearance of normal and abnormal cervical cells when examined with a microscope.
Cervical Cancer Prevalence and Death Rates
Worldwide, cervical cancer is the second most common type of cancer in females (after breast cancer) and the fourth-most common cause of cancer death in females. In Canada and other high-income nations, the widespread use of cervical cancer screening has detected many cases of precancerous cervical changes and has dramatically reduced rates of cervical cancer deaths. About 75% of cervical cancer cases occur in developing countries, where routine screening is less likely because of cost and other factors. Cervical cancer is also the most common cause of cancer death in low-income countries.
Symptoms of Cervical Cancer
Early in the development of cervical cancer, there are typically no symptoms. As the disease progresses, however, symptoms are likely to occur. The symptoms may include abnormal vaginal bleeding, pelvic pain, or pain during sexual intercourse. Unfortunately, by the time symptoms start to occur, cervical cancer has typically progressed to a stage at which treatment is less likely to be successful.
Cervical Cancer Causes and Risk Factors
More than 90 per cent of cases of cervical cancer are caused at least in part by human papillomavirus (HPV), which is a sexually transmitted virus that also causes genital warts. Figure 18.9.3 shows how HPV infection can cause cervical cancer by interfering with a normal cell division checkpoint. When HPV is not present, cervical cells containing mutations are not allowed to divide, so the cervix remains healthy. When HPV is present, however, cervical cells with mutations may be allowed to divide, leading to uncontrolled growth of mutated cells and the formation of a tumor.
Other risk factors for cervical cancer include smoking, a weakened immune system (for example, due to HIV infection), use of birth control pills, becoming sexually active at a young age, and having many sexual partners. However, these risk factors are less important than HPV infection. Instead, the risk factors are more likely to increase the risk of cervical cancer in females who are already infected with HPV. For example, among HPV-infected women, current and former smokers have roughly two to three times the incidence of cervical cancer as non-smokers. Passive smoking, or secondhand smoke, is also associated with an increased risk of cervical cancer, but to a lesser extent.
Diagnosis of Cervical Cancer
Diagnosis of cervical cancer is typically made by looking for microscopic abnormal cervical cells in a smear of cells scraped off the cervix. This is called a Pap smear. If cancerous cells are detected or suspected in the smear, this test is usually followed up with a biopsy to confirm the Pap smear results. Medical imaging (by CT scan or MRI, for example) is also likely to be done to provide more information, such as whether the cancer has spread.
Prevention of Cervical Cancer
It is now possible to prevent HPV infection with a vaccine. The first HPV vaccine was approved by the U.S. Food and Drug Administration in 2006. The vaccine protects against the strains of HPV that have the greatest risk of causing cervical cancer. It is thought that widespread use of the vaccine will prevent up to 90% of cervical cancer cases. Current recommendations are for females to be given the vaccine between the ages of nine and 26. (Boys should be vaccinated against HPV, as well, because the virus may also cause cancer of the penis and certain other male cancers.) The vaccine is effective only if it is given before HPV infection has occurred. Using condoms during sexual intercourse can also help prevent HPV infection and cervical cancer, in addition to preventing pregnancy and sexually transmitted infections (such as HIV).
Even in women who have received the HPV vaccine, there is still a small risk of developing cervical cancer. Therefore, it is recommended that women continue to be examined with regular Pap smears.
Treatment of Cervical Cancer
Treatment of cervical cancer generally depends on the stage at which the cancer is diagnosed, but it is likely to include some combination of surgery, radiation therapy, and/or chemotherapy. Outcomes of treatment depend largely on how early the cancer is diagnosed and treated. For surgery to cure cervical cancer, the entire tumor must be removed with no cancerous cells found at the margins of the removed tissue on microscopic examination. If cancer is found and treated very early when it is still in the microscopic stage, the five-year survival rate is virtually 100%.
Vaginitis
Vaginitis is inflammation of the vagina — and sometimes the vulva, as well. Symptoms may include a discharge that is yellow, gray, or green; itching; pain; and a burning sensation. There may also be a foul vaginal odor and pain or irritation with sexual intercourse.
Causes of Vaginitis
About 90% of cases of vaginitis are caused by infection with microorganisms. Most commonly, vaginal infections are caused by the yeast Candida albicans (see Figure 18.9.4). Such infections are referred to as vaginal candidiasis or more commonly as a yeast infection. Candida albicans is one of the most common opportunistic infections in the world and can affect not only the vagina, but any of the mucus membranes and skin. Other possible causes of vaginal infections include bacteria, especially Gardnerella vaginalis, and some single-celled parasites, notably the protist parasite Trichomonas vaginalis, which is usually transmitted through vaginal intercourse. The risk of vaginal infections may be greater in women who wear tight clothing, are taking antibiotics for another condition, use birth control pills, or have improper hygiene. Poor hygiene allows organisms that are normally present in the stool (such as yeast) to contaminate the vagina.
Most of the remaining cases of vaginitis are due to irritation by — or allergic reactions to — various products. These irritants may include condoms, spermicides, soaps, douches, lubricants, and even semen. Using tampons or soaking in hot tubs may be additional causes of this type of vaginitis.
Diagnosis of Vaginitis
Diagnosis of vaginitis typically begins with symptoms reported by the patient. This may be followed by a microscopic examination or culture of the vaginal discharge in order to identify the specific cause. The colour, consistency, acidity, and other characteristics of the discharge may be predictive of the causative agent. For example, infection with Candida albicans may cause a cottage cheese-like discharge with a low pH, whereas infection with Gardnerella vaginalis may cause a discharge with a fish-like odor and a high pH.
Prevention of Vaginitis
Prevention of vaginitis includes wearing loose cotton underwear that helps keep the vulva dry. Yeasts and bacteria that may cause vaginitis tend to grow best in a moist environment. It is also important to avoid the use of perfumed soaps, personal hygiene sprays, and douches, all of which may upset the normal pH and bacterial balance in the vagina. To help avoid vaginitis caused by infection with Trichomonas vaginalis, the use of condoms during sexual intercourse is advised.
Treatment of Vaginitis
The appropriate treatment of vaginitis depends on the cause. In many cases of vaginitis, there is more than one cause, and all of the causes must be treated to ensure a cure.
- Yeast infections of the vagina are typically treated with topical anti-fungal medications, which are available over the counter. The medications may be in the form of tablets or creams that are inserted into the vagina. Depending on the particular medication used, treatment may involve one, three, or seven days of applications.
- Bacterial infections of the vagina are usually treated with antibiotics. These may be taken orally as pills, or applied topically to the vagina in creams.
- Trichomonas vaginalis infections of the vagina are generally treated with a single dose of an oral antibiotic. Sexual partners should be treated at the same time, and intercourse should be avoided for at least a week until both partners have completed treatment, and have been followed-up by a physician.
Endometriosis
Endometriosis is a disease in which endometrial tissue, which normally grows inside the uterus, grows outside it, as shown in Figure 18.9.5. Most often, the endometrial tissue grows around the ovaries, Fallopian tubes, and uterus. In rare instances, the tissue may grow elsewhere in the body. The areas of endometriosis typically bleed each month during the menstrual period, and this often results in inflammation, pain, and scarring. An estimated six to ten per cent of women are believed to have endometriosis. It is most common in women during their thirties and forties, and only rarely occurs before menarche or after menopause.
Signs and Symptoms of Endometriosis
The main symptom of endometriosis is pelvic pain, which may range from mild to severe. There appears to be little or no relationship between the amount of endometrial tissue growing outside the uterus and the severity of the pain. For many women with the disease, the pain occurs mainly during menstruation. However, nearly half of those affected have chronic pelvic pain. The pain of endometriosis may be caused by bleeding in the pelvis, which triggers inflammation. Pain can also occur from internal scar tissue that binds internal organs to each other.
Another problem often associated with endometriosis is infertility, or the inability to conceive or bear children. Among women with endometriosis, up to half may experience infertility. Infertility can be related to scar formation or to anatomical distortions due to the abnormal endometrial tissue. Other possible symptoms of endometriosis may include diarrhea or constipation, chronic fatigue, nausea and vomiting, headaches, and heavy or irregular menstrual bleeding.
Causes of Endometriosis
The causes of endometriosis are not known for certain, but several risk factors have been identified, including a family history of endometriosis. Daughters or sisters of women with endometriosis have about six times the normal risk of developing the disease themselves. It has been suggested that endometriosis results from mutations in several genes. It is likely that endometriosis is multifactorial, involving the interplay of several factors.
At the physiological level, the predominant idea for how endometriosis comes about is retrograde menstruation. This happens when some of the endometrial debris from a woman’s menstrual flow exits the uterus through the oviducts, rather than through the vagina. The debris then attaches itself to the outside of organs in the abdominal cavity, or to the lining of the abdominal cavity itself. Retrograde menstruation, however, does not explain all cases of endometriosis, so other factors are apparently involved. Suggestions include environmental toxins and autoimmune responses.
Diagnosis of Endometriosis
Diagnosis of endometriosis is usually based on self-reported symptoms and a physical examination by a doctor, often combined with medical imaging, such as ultrasonography. The only way to definitively diagnose endometriosis, however, is through visual inspection of the endometrial tissue. This can be done with a surgical procedure called laparoscopy, shown in Figure 18.9.6, in which a tiny camera is inserted into the abdomen through a small incision. The camera allows the physician to visually inspect the area where endometrial tissue is suspected.
Treatment of Endometriosis
The most common treatments for endometriosis are medications to control the pain, and surgery to remove the abnormal tissue. Frequently used pain medications are non-steroidal inflammatory drugs (NSAIDS), such as naproxen. Opiates may be used in cases of severe pain. Laparoscopy can be used to surgically treat endometriosis, as well as to diagnose the condition. In this type of surgery, an additional small incision is made to insert instruments that the surgeon can manipulate externally in order to burn (cauterize) or cut away the endometrial growths. In younger women who want to have children, surgery is conservative to keep the reproductive organs intact and functional. However, with conservative surgery, endometriosis recurs in 20–40% of cases within five years of the surgery. In older women who have completed childbearing, hysterectomy may be undertaken to remove all or part of the internal reproductive organs. This is the only procedure that is likely to cure endometriosis and prevent relapses.
Feature: My Human Body
A Pap smear is a method of cervical cancer screening used to detect potentially pre-cancerous and cancerous cells in the cervix. It is the most widely used screening test for this type of cancer, and it is very effective. The test may also detect vaginal infections and abnormal endometrial cells, but it is not designed for these purposes.
According to HealthLink BC, females should start receiving routine Pap smears by age 25. Because most cases of cervical cancer are caused by infection with human papillomavirus (HPV), which is a sexually transmitted infection, there is little or no benefit to screening people who have not had sexual contact. Starting at age 25, general guidelines are for Pap smears to be repeated every three years until age 69. Screening may be discontinued after 69 years of age, if the last three Pap smears were normal. If a woman has a complete hysterectomy, she no longer has a cervix and there is no need for further Pap smears. On the other hand, if a woman has had a history of abnormal Pap smears or cancer, she will likely be screened more frequently. Pap smears can be done safely during the first several months of pregnancy, and resumed about three months after childbirth. Generally, better results are obtained if Pap smears are not done during menstruation.
If you’ve never had a Pap smear, knowing what to expect may help prepare you for the procedure. The patient lies on the examining table with her feet in “stirrups” to hold the legs up and apart. An instrument called a speculum is inserted into the vagina to hold back the vaginal walls and give access to the cervix. A tiny amount of tissue is brushed off the cervix and smeared onto a microscope slide. The speculum is then removed, and the procedure is over. The slide is later examined under a microscope for abnormal cells. Some women experience light spotting or mild diarrhea after a Pap smear, but most have no lasting effects.
Pap smears are uncomfortable and may be somewhat painful for some women. If you experience pain during a Pap smear, tell your health care provider. Many steps can be taken to minimize the pain, which might include using a smaller speculum, using warm instruments and a lubricant, and applying a topical anesthetic such as lidocaine to the cervix before obtaining the smear. Any pain is generally very brief, and the potential reward is worth it. Pap tests are estimated to reduce up to 80% of cervical cancer deaths. One of the lives saved could be your own.
18.9 Summary
- Cervical cancer occurs when cells of the cervix grow abnormally and develop the ability to invade nearby tissues or spread to other parts of the body. Worldwide, cervical cancer is the second-most common type of cancer in females and the fourth-most common cause of cancer death in females. Early on, cervical cancer often has no symptoms. Later, symptoms (such as abnormal vaginal bleeding and pain) are likely.
- Most cases of cervical cancer occur because of infection with human papillomavirus (HPV), so the HPV vaccine is expected to greatly reduce the incidence of the disease. Other risk factors include smoking and a weakened immune system. A Pap smear can diagnose cervical cancer at an early stage. Where Pap smears are done routinely, cervical cancer death rates have fallen dramatically. Treatment of cervical cancer generally includes surgery, which may be followed by radiation therapy or chemotherapy.
- Vaginitis is inflammation of the vagina. A discharge is likely, and there may be itching and pain. About 90% of cases of vaginitis are caused by infection with microorganisms, typically by the yeast Candida albicans. A minority of cases are caused by irritants or allergens in soaps, spermicides, or douches.
- Diagnosis of vaginitis may be based on characteristics of the discharge, which can be examined microscopically or cultured. Treatment of vaginitis depends on the cause and is usually an oral or topical anti-fungal or antibiotic medication.
- Endometriosis is a disease in which endometrial tissue grows outside the uterus. This tissue may bleed during the menstrual period and cause inflammation, pain, and scarring. The main symptom of endometriosis is pelvic pain, which may be severe. Endometriosis may also lead to infertility.
- Endometriosis is thought to have multiple causes, including genetic mutations. Retrograde menstruation may be the immediate cause of endometrial tissue escaping the uterus and entering the pelvic cavity. Endometriosis is usually treated with surgery to remove the abnormal tissue and medication for pain. If surgery is more conservative than hysterectomy, endometriosis may recur.
18.9 Review Questions
- What is cervical cancer? Worldwide, how prevalent is it, and how does it rank as a cause of cancer deaths?
- Identify symptoms of cervical cancer. What are causes of — and risk factors for — cervical cancer?
- What roles can Pap smears and HPV vaccines play in preventing cervical cancer cases and cervical cancer deaths?
- How is cervical cancer treated?
- Define vaginitis and identify its symptoms.
- What are some of the causes of vaginitis? Which cause is responsible for most of the cases?
- How is vaginitis diagnosed and treated?
- What is endometriosis, and what are its symptoms?
- Discuss possible causes of endometriosis.
- How is endometriosis treated? Which treatment is most likely to prevent recurrence of the disorder?
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- In the case of infection with Trichomonas vaginalis, why is the woman’s sexual partner usually treated at the same time?
18.9 Explore More
What is HPV and how can you protect yourself from it? – Emma Bryce, TED-Ed, 2019.
Endometriosis – The Mystery Disease of Women | Cécile Real | TEDxBinnenhof, TEDx Talks, 2016.
The brain and ovarian hormones | Marwa Azab | TEDxMontrealWomen, TEDxTalks, 2015.
Attributions
Figure 18.9.1
a-nurse-giving-a-young-girl-a-vaccine-shot-or by CDC/ Judy Schmidt from Public Health Image Library (PHIL) #9424 is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 18.9.2
1024px-Blausen_0221_CervicalDysplasia by Blausen Medical Communications, Inc. on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.9.3
HPV and Cervical Cancer by OpenStax by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.9.4
Candida by NIH on Flickr from the NIH Image Gallery on Flickr is used under a CC BY NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 18.9.5
Blausen_0349_Endometriosis by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.9.6
1024px-Blausen_0602_Laparoscopy_02 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 27.16 Development of cervical cancer [digital image]. In Anatomy and Physiology (Section 27.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/27-2-anatomy-and-physiology-of-the-female-reproductive-system
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
HealthLink BC. (n.d.). Pap test: British Columbia specific information. https://www.healthlinkbc.ca/medical-tests/hw5266
TED-Ed. (2019, July 9). What is HPV and how can you protect yourself from it? – Emma Bryce. YouTube. https://www.youtube.com/watch?v=KOz-bNhEHhQ&feature=youtu.be
TEDx Talks. (2016, April 14). Endometriosis – The mystery disease of women | Cécile Real | TEDxBinnenhof. YouTube. https://www.youtube.com/watch?v=6HeQ4iEqAUk&feature=youtu.be
TEDx Talks. (2015, July 27). The brain and ovarian hormones | Marwa Azab | TEDxMontrealWomen. YouTube. https://www.youtube.com/watch?v=ryNjSP5VVI8&feature=youtu.be
A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.
Image shows a photomicrograph of a sperm fertilizing an egg.
Image shows a side view diagram of the male and female pelvis. The male urethra is much longer because it extends through the penis, and in women it exits through the pelvic floor.
Image shows a diagram labeling the major arteries of the body. Some of these include the carotid artery which provides blood to the neck and head, the brachiocephalic artery which supplies blood to the arms and head, the renal artery supplying blood to the kidneys, the mesenteric arteries supplying blood to the intestines, the femoral arteries supplying blood to the legs.
Created by CK-12 Foundation/Adapted by Christine Miller
It’s All about Sex
A tiny sperm from dad breaks through the surface of a huge egg from mom. Voilà! In nine months, a new son or daughter will be born. Like most other multicellular organisms, human beings reproduce sexually. In human sexual reproduction, males produce sperm and females produce eggs, and a new offspring forms when a sperm unites with an egg. How do sperm and eggs form? And how do they arrive together at the right place and time so they can unite to form a new offspring? These are functions of the reproductive system.
What Is the Reproductive System?
The reproductive system is the human organ system responsible for the production and fertilization of gametes (sperm or eggs) and, in females, the carrying of a fetus. Both male and female reproductive systems have organs called gonads that produce gametes. A gamete is a haploid cell that combines with another haploid gamete during fertilization, forming a single diploid cell called a zygote. Besides producing gametes, the gonads also produce sex hormones. Sex hormones are endocrine hormones that control the development of sex organs before birth, sexual maturation at puberty, and reproduction once sexual maturation has occurred. Other reproductive system organs have various functions, such as maturing gametes, delivering gametes to the site of fertilization, and providing an environment for the development and growth of an offspring.
Sex Differences in the Reproductive System
The reproductive system is the only human organ system that is significantly different between males and females. Embryonic structures that will develop into the reproductive system start out the same in males and females, but by birth, the reproductive systems have differentiated. How does this happen?
Sex Differentiation
Starting around the seventh week after conception in genetically male (XY) embryos, a gene called SRY on the Y chromosome (shown in Figure 18.2.2) initiates the production of multiple proteins. These proteins cause undifferentiated gonadal tissue to develop into male gonads (testes). The male gonads then secrete hormones — including the male sex hormone testosterone — that trigger other changes in the developing offspring (now called a fetus), causing it to develop a complete male reproductive system. Without a Y chromosome, an embryo will develop female gonads (ovaries) that will produce the female sex hormone estrogen. Estrogen, in turn, will lead to the formation of the other organs of a normal female reproductive system.
Homologous Structures
Undifferentiated embryonic tissues develop into different structures in male and female fetuses. Structures that arise from the same tissues in males and females are called homologous structures. The male testes and female ovaries, for example, are homologous structures that develop from the undifferentiated gonads of the embryo. Likewise, the male penis and female clitoris are homologous structures that develop from the same embryonic tissues.
Sex Hormones and Maturation
Male and female reproductive systems are different at birth, but they are immature and incapable of producing gametes or sex hormones. Maturation of the reproductive system occurs during puberty, when hormones from the hypothalamus and pituitary gland stimulate the testes or ovaries to start producing sex hormones again. The main sex hormones are testosterone in males and estrogen in females. Sex hormones, in turn, lead to the growth and maturation of the reproductive organs, rapid body growth, and the development of secondary sex characteristics. Secondary sex characteristics are traits that are different in mature males and females, but are not directly involved in reproduction. They include facial hair in males and breasts in females.
Male Reproductive System
The main structures of the male reproductive system are external to the body and illustrated in Figure 18.2.3. The two testes (singular, testis) hang between the thighs in a sac of skin called the scrotum. The testes produce both sperm and testosterone. Resting atop each testis is a coiled structure called the epididymis (plural, epididymes). The function of the epididymes is to mature and store sperm. The penis is a tubular organ that contains the urethra and has the ability to stiffen during sexual arousal. Sperm passes out of the body through the urethra during a sexual climax (orgasm). This release of sperm is called ejaculation.
In addition to these organs, the male reproductive system consists of several ducts and glands that are internal to the body. The ducts, which include the vas deferens (also called the ductus deferens), transport sperm from the epididymis to the urethra. The glands, which include the prostate gland and seminal vesicles, produce fluids that become part of semen. Semen is the fluid that carries sperm through the urethra and out of the body. It contains substances that control pH and provide sperm with nutrients for energy.
Female Reproductive System
The main structures of the female reproductive system are internal to the body and shown in the following figure. They include the paired ovaries, which are small, ovoid structures that produce ova and secrete estrogen. The two oviducts (sometimes called Fallopian tubes or uterine tubes) start near the ovaries and end at the uterus. Their function is to transport ova from the ovaries to the uterus. If an egg is fertilized, it usually occurs while it is traveling through an oviduct. The uterus is a pear-shaped muscular organ that functions to carry a fetus until birth. It can expand greatly to accommodate a growing fetus, and its muscular walls can contract forcefully during labour to push the baby out of the uterus and into the vagina. The vagina is a tubular tract connecting the uterus to the outside of the body. The vagina is where sperm are usually deposited during sexual intercourse and ejaculation. The vagina is also called the birth canal because a baby travels through the vagina to leave the body during birth.
The external structures of the female reproductive system are referred to collectively as the vulva. They include the clitoris, which is homologous to the male penis. They also include two pairs of labia (singular, labium), which surround and protect the openings of the urethra and vagina.
18.2 Summary
- The reproductive system is the human organ system responsible for the production and fertilization of gametes and, in females, the carrying of a fetus.
- Both male and female reproductive systems have organs called gonads (testes in males, ovaries in females) that produce gametes (sperm or ova) and sex hormones (such as testosterone in males and estrogen in females). Sex hormones are endocrine hormones that control the prenatal development of reproductive organs, sexual maturation at puberty, and reproduction after puberty.
- The reproductive system is the only organ system that is significantly different between males and females. A Y-chromosome gene called SRY is responsible for undifferentiated embryonic tissues developing into a male reproductive system. Without a Y chromosome, the undifferentiated embryonic tissues develop into a female reproductive system.
- Structures such as testes and ovaries that arise from the same undifferentiated embryonic tissues in males and females are called homologous structures.
- Male and female reproductive systems are different at birth, but at that point, they are immature and nonfunctioning. Maturation of the reproductive system occurs during puberty, when hormones from the hypothalamus and pituitary gland stimulate the gonads to produce sex hormones again. The sex hormones, in turn, cause the changes of puberty.
- Male reproductive system organs include the testes, epididymis, penis, vas deferens, prostate gland, and seminal vesicles.
- Female reproductive system organs include the ovaries, oviducts, uterus, vagina, clitoris, and labia.
18.2 Review Questions
- What is the reproductive system?
-
- Explain the difference between the vulva and the vagina.
18.2 Explore More
https://youtu.be/kMWxuF9YW38
Sex Determination: More Complicated Than You Thought, TED-Ed, 2012.
https://youtu.be/vcPJkz-D5II
The evolution of animal genitalia - Menno Schilthuizen, TED-Ed, 2017.
https://youtu.be/l5knvmy1Z3s
Hormones and Gender Transition, Reactions, 2015.
Attributions
Figure 18.2.1
Sperm-egg by Unknown author on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain).
Figure 18.2.2
Y Chromosome by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.2.3
3D_Medical_Animation_Vas_Deferens by https://www.scientificanimations.com on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.2.4
Blausen_0399_FemaleReproSystem_01 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
Reactions. (2015, June 8). Hormones and gender transition. YouTube. https://www.youtube.com/watch?v=l5knvmy1Z3s&feature=youtu.be
TED-Ed. (2012, April 23). Sex determination: More complicated than you thought. YouTube. https://www.youtube.com/watch?v=kMWxuF9YW38&feature=youtu.be
TED-Ed. (2017, April 24). The evolution of animal genitalia - Menno Schilthuizen. YouTube. https://www.youtube.com/watch?v=vcPJkz-D5II&feature=youtu.be
Image shows a labelled diagram of the male reproductive system. Hanging below the pelvic cavity is the scrotum, which contains the testes and epididymis. A vas deferens leads away from each testis and up into the pelvic cavity to eventually merge with the urinary urethra, which travels through the penis. There are several glands associated with the male reproductive tract, including the prostate gland, Cowper's gland, and seminal vesicles.
Case Study: Cough That Won't Quit
Three weeks ago, 20-year-old Erica came down with symptoms typical of the common cold. She had a runny nose, fatigue, and a mild cough. Her symptoms were starting to improve, but recently, her cough has been getting worse. She is coughing up a lot of thick mucus, her throat is sore from frequent coughing, and her chest feels very congested. According to her grandmother, Erica has a “chest cold.” Erica is a smoker and wonders if her habit is making her cough worse. She decides that it's time to see a doctor.
Dr. Choo examines Erica and asks about her symptoms and health history. She checks the level of oxygen in Erica’s blood by attaching a device called a pulse oximeter to Erica’s finger.
Dr. Choo concludes that Erica has bronchitis, which is an infection that commonly occurs after a person has a cold or flu. Bronchitis is sometimes referred to as a “chest cold,” so Erica’s grandmother was right! Bronchitis causes inflammation and a build up of mucus in the bronchial tubes in the chest.
Because bronchitis is usually caused by viruses and not bacteria, Dr. Choo tells Erica that antibiotics are not likely to help. Instead, she recommends that Erica try to thin out and remove the mucus by drinking plenty of fluids and using a humidifier or spending time in a steamy shower. She recommends that Erica get plenty of rest as well.
Dr. Choo also tells Erica some things not to do — most importantly, to stop smoking while she is sick, and to try to quit smoking in the long-term. She explains that smoking can make people more susceptible to bronchitis and can hinder recovery. Finally, she advises Erica to avoid taking over-the-counter cough suppressant medication.
As you read this chapter about the respiratory system, you will be able to better understand what bronchitis is, and why Dr. Choo made the treatment recommendations that she did. At the end of the chapter, you will learn more about acute bronchitis, which is the type that Erica has. This information may come in handy to you personally, because chances are high that you will get this common infection at some point in your life — there are millions of cases of bronchitis every year!
Chapter Overview: Respiratory System
In this chapter, you will learn about the respiratory system — the system that exchanges gases (such as oxygen and carbon dioxide) between the body and the outside air. Specifically, you will learn about:
- The process of respiration, in which oxygen moves from the outside air into the body and carbon dioxide and other waste gases move from inside the body into the outside air.
- The organs of the respiratory system, including the lungs, bronchial tubes, and the rest of the respiratory tract.
- How the respiratory tract protects itself from pathogens and other potentially harmful substances in the air.
- How the rate of breathing is regulated to maintain homeostasis of blood gases and pH.
- How ventilation, or breathing, allows us to inhale air into the body and exhale air out of the body.
- The conscious and unconscious control of breathing.
- Nasal breathing compared to mouth breathing.
- What happens when a person is drowning.
- How gas exchange occurs between the air and blood in the alveoli of the lungs, and between the blood and cells throughout the body.
- Disorders of the respiratory system, including asthma, pneumonia, chronic obstructive pulmonary disease (COPD), and lung cancer.
- The negative health effects of smoking.
As you read the chapter, think about the following questions:
- Where are the bronchial tubes? What is their function?
- What is the function of mucus? Why can too much mucus be a bad thing?
- Why did Dr. Choo check Erica’s blood oxygen level?
- Why do you think Dr. Choo warned Erica to avoid cough suppressant medications?
- How does acute bronchitis compare to chronic bronchitis? How do they both relate to smoking?
Attributions
Figure 13.1.1
Cold/ Look into my eyes forever [photo] by Spencer Backman on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 13.1.2
Wrist-oximeter by UusiAjaja on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/deed.en) license.
Reference
Mayo Clinic Staff. (n.d.). Bronchitis [online article]. Mayoclinic.org. https://www.mayoclinic.org/diseases-conditions/bronchitis/symptoms-causes/syc-20355566
As per caption.
We All Scream for Ice Cream
If you’re an ice cream lover, then just the sight of this yummy ice cream cone may make your mouth water. The “water” in your mouth is actually saliva, a fluid released by glands that are part of the digestive system. Saliva contains digestive enzymes, among other substances important for digestion. When your mouth waters at the sight of a tasty treat, it’s a sign that your digestive system is preparing to digest food.
What Is the Digestive System?
The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste. Organs of the digestive system are shown in Figure 15.2.2. Most of these organs make up the gastrointestinal (GI) tract, through which food actually passes. The rest of the organs of the digestive system are called accessory organs. These organs secrete enzymes and other substances into the GI tract, but food does not actually pass through them.
Functions of the Digestive System
The digestive system has three main functions relating to food: digestion of food, absorption of nutrients from food, and elimination of solid food waste. Digestion is the process of breaking down food into components the body can absorb. It consists of two types of processes: mechanical digestion and chemical digestion. Mechanical digestion is the physical breakdown of chunks of food into smaller pieces, and it takes place mainly in the mouth and stomach. Chemical digestion is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by body fluids (blood or lymph). This type of digestion begins in the mouth and continues in the stomach, but occurs mainly in the small intestine.
After food is digested, the resulting nutrients are absorbed. Absorption is the process in which substances pass into the bloodstream or lymph system to circulate throughout the body. Absorption of nutrients occurs mainly in the small intestine. Any remaining matter from food that is not digested and absorbed passes out of the body through the anus in the process of elimination.
Gastrointestinal Tract
The gastrointestinal (GI) tract is basically a long, continuous tube that connects the mouth with the anus. If it were fully extended, it would be about nine metres long in adults. It includes the mouth, pharynx, esophagus, stomach, and small and large intestines. Food enters the mouth, and then passes through the other organs of the GI tract, where it is digested and/or absorbed. Finally, any remaining food waste leaves the body through the anus at the end of the large intestine. It takes up to 50 hours for food or food waste to make the complete trip through the GI tract.
Tissues of the GI Tract
The walls of the organs of the GI tract consist of four different tissue layers, which are illustrated in Figure 15.2.3: mucosa, submucosa, muscularis externa, and serosa.
- The mucosa is the innermost layer surrounding the lumen (open space within the organs of the GI tract). This layer consists mainly of epithelium with the capacity to secrete and absorb substances. The epithelium can secret digestive enzymes and mucus, and it can absorb nutrients and water.
- The submucosa layer consists of connective tissue that contains blood and lymph vessels, as well as nerves. The vessels are needed to absorb and carry away nutrients after food is digested, and nerves help control the muscles of the GI tract organs.
- The muscularis externa layer contains two types of smooth muscle: longitudinal muscle and circular muscle. Longitudinal muscle runs the length of the GI tract organs, and circular muscle encircles the organs. Both types of muscles contract to keep food moving through the tract by the process of peristalsis, which is described below.
- The serosa layer is the outermost layer of the walls of GI tract organs. This is a thin layer that consists of connective tissue and separates the organs from surrounding cavities and tissues.
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Peristalisis in the GI Tract
The muscles in the walls of GI tract organs enable peristalsis, which is illustrated in Figure 15.2.5. Peristalsis is a continuous sequence of involuntary muscle contraction and relaxation that moves rapidly along an organ like a wave, similar to the way a wave moves through a spring toy. Peristalsis in organs of the GI tract propels food through the tract.
Watch the video "What is peristalsis?" by Mister Science to see peristalsis in action:
https://youtu.be/kVjeNZA5pi4
What is peristalsis?, Mister Science, 2018.
Immune Function of the GI Tract
The GI tract plays an important role in protecting the body from pathogens. The surface area of the GI tract is estimated to be about 32 square metres (105 square feet), or about half the area of a badminton court. This is more than three times the area of the exposed skin of the body, and it provides a lot of area for pathogens to invade the tissues of the body. The innermost mucosal layer of the walls of the GI tract provides a barrier to pathogens so they are less likely to enter the blood or lymph circulations. The mucus produced by the mucosal layer, for example, contains antibodies that mark many pathogenic microorganisms for destruction. Enzymes in some of the secretions of the GI tract also destroy pathogens. In addition, stomach acids have a very low pH that is fatal for many microorganisms that enter the stomach.
Divisions of the GI Tract
The GI tract is often divided into an upper GI tract and a lower GI tract. For medical purposes, the upper GI tract is typically considered to include all the organs from the mouth through the first part of the small intestine, called the duodenum. For our instructional purposes, it makes more sense to include the mouth through the stomach in the upper GI tract, and all of the small intestine — as well as the large intestine — in the lower GI tract.
Upper GI Tract
The mouth is the first digestive organ that food enters. The sight, smell, or taste of food stimulates the release of digestive enzymes and other secretions by salivary glands inside the mouth. The major salivary gland enzyme is amylase. It begins the chemical digestion of carbohydrates by breaking down starches into sugar. The mouth also begins the mechanical digestion of food. When you chew, your teeth break, crush, and grind food into increasingly smaller pieces. Your tongue helps mix the food with saliva and also helps you swallow.
A lump of swallowed food is called a bolus. The bolus passes from the mouth into the pharynx, and from the pharynx into the esophagus. The esophagus is a long, narrow tube that carries food from the pharynx to the stomach. It has no other digestive functions. Peristalsis starts at the top of the esophagus when food is swallowed and continues down the esophagus in a single wave, pushing the bolus of food ahead of it.
From the esophagus, food passes into the stomach, where both mechanical and chemical digestion continue. The muscular walls of the stomach churn and mix the food, thus completing mechanical digestion, as well as mixing the food with digestive fluids secreted by the stomach. One of these fluids is hydrochloric acid (HCl). In addition to killing pathogens in food, it gives the stomach the low pH needed by digestive enzymes that work in the stomach. One of these enzymes is pepsin, which chemically digests proteins. The stomach stores the partially digested food until the small intestine is ready to receive it. Food that enters the small intestine from the stomach is in the form of a thick slurry (semi-liquid) called chyme.
Lower GI Tract
The small intestine is a narrow, but very long tubular organ. It may be almost seven metres long in adults. It is the site of most chemical digestion and virtually all absorption of nutrients. Many digestive enzymes are active in the small intestine, some of which are produced by the small intestine itself, and some of which are produced by the pancreas, an accessory organ of the digestive system. Much of the inner lining of the small intestine is covered by tiny finger-like projections called villi, each of which is covered by even tinier projections called microvilli. These projections, shown in the drawing below (Figure 15.2.6), greatly increase the surface area through which nutrients can be absorbed from the small intestine.
From the small intestine, any remaining nutrients and food waste pass into the large intestine. The large intestine is another tubular organ, but it is wider and shorter than the small intestine. It connects the small intestine and the anus. Waste that enters the large intestine is in a liquid state. As it passes through the large intestine, excess water is absorbed from it. The remaining solid waste — called feces — is eventually eliminated from the body through the anus.
Accessory Organs of the Digestive System
Accessory organs of the digestive system are not part of the GI tract, so they are not sites where digestion or absorption take place. Instead, these organs secrete or store substances needed for the chemical digestion of food. The accessory organs include the liver, gallbladder, and pancreas. They are shown in Figure 15.2.7 and described in the text that follows.
- The liver is an organ with multitude of functions. Its main digestive function is producing and secreting a fluid called bile, which reaches the small intestine through a duct. Bile breaks down large globules of lipids into smaller ones that are easier for enzymes to chemically digest. Bile is also needed to reduce the acidity of food entering the small intestine from the highly acidic stomach, because enzymes in the small intestine require a less acidic environment in order to work.
- The gallbladder is a small sac below the liver that stores some of the bile from the liver. The gallbladder also concentrates the bile by removing some of the water from it. It then secretes the concentrated bile into the small intestine as needed for fat digestion following a meal.
- The pancreas secretes many digestive enzymes, and releases them into the small intestine for the chemical digestion of carbohydrates, proteins, and lipids. The pancreas also helps lessen the acidity of the small intestine by secreting bicarbonate, a basic substance that neutralizes acid.
15.2 Summary
- The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining food waste.
- Digestion is the process of breaking down food into components that the body can absorb. It includes mechanical digestion and chemical digestion. Absorption is the process of taking up nutrients from food by body fluids for circulation to the rest of the body. Elimination is the process of excreting any remaining food waste after digestion and absorption are finished.
- Most digestive organs form a long, continuous tube called the gastrointestinal (GI) tract. It starts at the mouth, which is followed by the pharynx, esophagus, stomach, small intestine, and large intestine. The upper GI tract consists of the mouth through the stomach, while the lower GI tract consists of the small and large intestines.
- Digestion and/or absorption take place in most of the organs of the GI tract. Organs of the GI tract have walls that consist of several tissue layers that enable them to carry out these functions. The inner mucosa has cells that secrete digestive enzymes and other digestive substances, as well as cells that absorb nutrients. The muscle layer of the organs enables them to contract and relax in waves of peristalsis to move food through the GI tract.
- Three digestive organs — the liver, gallbladder, and pancreas — are accessory organs of digestion. They secrete substances needed for chemical digestion into the small intestine.
15.2 Review Questions
- What is the digestive system?
- What are the three main functions of the digestive system? Define each function.
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- Relate the tissues in the walls of GI tract organs to the functions the organs perform.
15.2 Explore More
https://youtu.be/Og5xAdC8EUI
How your digestive system works - Emma Bryce, TED-Ed, 2017.
https://youtu.be/YVfyYrEmzgM
How does your body know you're full? - Hilary Coller, TED-Ed, 2017.
Attributions
Figure 15.2.1
Ice Cream [photo] by Mark Cruz on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 15.2.2
Blausen_0316_DigestiveSystem by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 15.2.3
Intestinal_layers by Boumphreyfr on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.
Figure 15.2.4
512px-Normal_gastric_mucosa_intermed_mag by Nephron on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.
Figure 15.2.5
Peristalsis pushes food through the GI tract by CK-12 Foundation is used under a CC BY NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
Figure 15.2.6
Villi_&_microvilli_of_small_intestine.svg by BallenaBlanca on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 15.2.7
Blausen_0428_Gallbladder-Liver-Pancreas_Location by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
Brainard, J/ CK-12 Foundation. (2016). Figure 4 Peristalsis pushes food through the GI tract. [digital image]. In CK-12 College Human Biology (Section 17.2) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/17.2/
Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/channel/UCxTlkZfjArUobBAeVwzJjYg/videos
TED-Ed. (2017, November 13). How does your body know you're full? - Hilary Coller. YouTube. https://www.youtube.com/watch?v=YVfyYrEmzgM&feature=youtu.be
TED-Ed. (2017, December 14). How your digestive system works - Emma Bryce. YouTube. https://www.youtube.com/watch?v=Og5xAdC8EUI&feature=youtu.be
Image shows a diagram illustrating how peristalsis pushes food through the digestive tract by squeezing just behind the food, pushing it forward.
An organisms that is so small it is invisible to the human eye.
Image shows a cross-sectional diagram of the penis. The urethra is actually located, not in the centre, but nearer the bottom of the structure. Above that are two deep arteries, and near the top are two veins. Surrounding the arteries is the corpus cavernosum. Surrounding the urethra is the corpous spongiosum.
What Are You Made of?
Your entire body is made of cells and cells are made of molecules.If you look at your hand, what do you see? Of course, you see skin, which consists of cells. But what are skin cells made of? Like all living cells, they are made of matter. In fact, all things are made of matter. Matter is anything that takes up space and has mass. Matter, in turn, is made up of chemical substances. A chemical substance is matter that has a definite composition that is consistent throughout. A chemical substance may be either an element or a compound.
Elements and Atoms
An element is a pure substance. It cannot be broken down into other types of substances. Each element is made up of just one type of atom.
Structure of an Atom
An atom is the smallest particle of an element that still has the properties of that element. Every substance is composed of atoms. Atoms are extremely small, typically about a ten-billionth of a metre in diametre. However, atoms do not have well-defined boundaries, as suggested by the atomic model shown below.
Every atom is composed of a central area — called the nucleus — and one or more subatomic particles called electrons, which move around the nucleus. The nucleus also consists of subatomic particles. It contains one or more protons and typically a similar number of neutrons. The number of protons in the nucleus determines the type of element an atom represents. An atom of hydrogen, for example, contains just one proton. Atoms of the same element may have different numbers of neutrons in the nucleus. Atoms of the same element with the same number of protons — but different numbers of neutrons — are called isotopes.
Protons have a positive electric charge and neutrons have no electric charge. Virtually all of an atom's mass is in the protons and neutrons in the nucleus. Electrons surrounding the nucleus have almost no mass, as well as a negative electric charge. If the number of protons and electrons in an atom are equal, then an atom is electrically neutral, because the positive and negative charges cancel each other out. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion.
The negatively-charged electrons of an atom are attracted to the positively-charged protons in the nucleus by a force called electromagnetic force, for which opposite charges attract. Electromagnetic force between protons in the nucleus causes these subatomic particles to repel each other, because they have the same charge. However, the protons and neutrons in the nucleus are attracted to each other by a different force, called nuclear force, which is usually stronger than the electromagnetic force. Nuclear force repels the positively-charged protons from each other.
Periodic Table of the Elements
There are almost 120 known elements. As you can see in the Periodic Table of the Elements shown below, the majority of elements are metals. Examples of metals are iron (Fe) and copper (Cu). Metals are shiny and good conductors of electricity and heat. Nonmetal elements are far fewer in number. They include hydrogen (H) and oxygen (O). They lack the properties of metals.
The periodic table of the elements arranges elements in groups based on their properties. The element most important to life is carbon (C). Find carbon in the table. What type of element is it: metal or nonmetal?
Compounds and Molecules
A compound is a unique substance that consists of two or more elements combined in fixed proportions. This means that the composition of a compound is always the same. The smallest particle of most compounds in living things is called a molecule.
Consider water as an example. A molecule of water always contains one atom of oxygen and two atoms of hydrogen. The composition of water is expressed by the chemical formula H2O. A model of a water molecule is shown in Figure 3.2.4.
What causes the atoms of a water molecule to “stick” together? The answer is chemical bonds. A chemical bond is a force that holds together the atoms of molecules. Bonds in molecules involve the sharing of electrons among atoms. New chemical bonds form when substances react with one another. A chemical reaction is a process that changes some chemical substances into others. A chemical reaction is needed to form a compound, and another chemical reaction is needed to separate the substances in that compound.
3.2 Summary
- All matter consists of chemical substances. A chemical substance has a definite composition which is consistent throughout. A chemical substance may be either an element or a compound.
- An element is a pure substance that cannot be broken down into other types of substances.
- An atom is the smallest particle of an element that still has the properties of that element. Atoms, in turn, are composed of subatomic particles, including negative electrons, positive protons, and neutral neutrons. The number of protons in an atom determines the element it represents.
- Atoms have equal numbers of electrons and protons, so they have no charge. Ions are atoms that have lost or gained electrons, and as a result have either a positive or negative charge. Atoms with the same number of protons — but different numbers of neutrons — are called isotopes.
- There are almost 120 known elements. The majority of elements are metals. A smaller number are nonmetals. The latter include carbon, hydrogen, and oxygen.
- A compound is a substance that consists of two or more elements in a unique composition. The smallest particle of a compound is called a molecule. Chemical bonds hold together the atoms of molecules. Compounds can form only in chemical reactions, and they can break down only in other chemical reactions.
3.2 Review Questions
-
- What is an element? Give three examples.
- Define compound. Explain how compounds form.
- Compare and contrast atoms and molecules.
- The compound called water can be broken down into its constituent elements by applying an electric current to it. What ratio of elements is produced in this process?
- Relate ions and isotopes to elements and atoms.
- What is the most important element to life?
- Iron oxide is often known as rust — the reddish substance you might find on corroded metal. The chemical formula for this type of iron oxide is Fe2O3. Answer the following questions about iron oxide and briefly explain each answer.
- Is iron oxide an element or a compound?
- Would one particle of iron oxide be considered a molecule or an atom?
- Describe the relative proportion of atoms in iron oxide.
- What causes the Fe and O to stick together in iron oxide?
- Is iron oxide made of metal atoms, metalloid atoms, nonmetal atoms, or a combination of any of these?
- 14C is an isotope of carbon used in the radiocarbon dating of organic material. The most common isotope of carbon is 12C. Do you think 14C and 12C have different numbers of neutrons or protons? Explain your answer.
- Explain why ions have a positive or negative charge.
- Name the three subatomic particles described in this section.
3.2 Explore More
https://www.youtube.com/watch?v=yQP4UJhNn0I&feature=emb_logo
Just how small is an atom? TED-Ed, 2012
Attributions
Figure 3.2.1
Man Sitting, by Gregory Culmer, on Unsplash, is used under the Unsplash license (https://unsplash.com/license).
Figure 3.2.2
Lithium Atom diagram, by AG Caesar, is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
Figure 3.2.3
Periodic Table Armtuk3, by Armtuk, is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/) license.
Figure 3.2.4
Water molecule, by Sakurambo, is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
TED-Ed. (2012, April 16). Just how small is an atom. YouTube. https://www.youtube.com/watch?v=yQP4UJhNn0I&feature=youtu.be
Rocky Mountain Oysters
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’t come from the sea. They may also be known as Montana tendergroin, cowboy caviar, or swinging beef — all names that hint at their origins. Here’s another hint: they are harvested only from male animals, such as bulls or sheep. What are they? In a word: testes.
Testes and Scrotum
The two testes (singular, testis) are sperm- and testosterone-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 pouch made of skin and smooth muscle that hangs down behind the penis.
Testes Structure
The testes are filled with hundreds of tiny tubes, called seminiferous tubules, 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).
Tunica
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).
- The tunica vasculosa is the innermost layer of the tunica. It consists of connective tissue and contains arteries and veins that carry blood to and from the testis.
- The tunica albuginea is 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.
- The tunica vaginalis is the outmost layer of the tunica. It actually consists of two layers of tissue separated by a thin fluid layer. The fluid reduces friction between the testes and the scrotum.
Seminiferous Tubules
One or more seminiferous tubules 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 cells. These cells release a hormone (inhibin) that helps regulate sperm production. Adjacent Sertoli cells are closely spaced so large molecules cannot pass from the blood into the tubules. This prevents the male’s immune system from reacting against the developing sperm, which may be antigenically different from his own self tissues. Cells of another type, called Leydig cells, are found between the seminiferous tubules. Leydig cells produce and secrete testosterone.
Other Scrotal Structures
Besides the two testes, the scrotum also contains a pair of organs called epididymes (singular, epididymis) and part of each of the paired vas deferens (or ducti deferens). Both structures play important functions in the production or transport of sperm.
Epididymis
The seminiferous tubules within each testis join together to form ducts (called efferent ducts) that transport immature sperm to the epididymis associated with that testis. Each epididymis (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 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.
Vas Deferens
The vas deferens, 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, and continue up into the pelvic cavity. They are composed of ciliated epithelium and smooth muscle. These structures help the vas deferens fulfill their function of transporting sperm from the epididymes to the ejaculatory ducts, which are accessory structures of the male reproductive system.
Accessory Structures
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’s) glands.
Seminal Vesicles
The seminal vesicles 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 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 semen, which is the sperm-containing fluid that leaves the penis during an ejaculation. The fluid from the seminal vesicles is alkaline, so it gives semen a basic pH that helps prolong the lifespan of sperm after it enters the acidic secretions inside the female vagina. Fluid from the seminal vesicles also contains proteins, fructose (a simple sugar), and other substances that help nourish sperm.
Ejaculatory Ducts
The ejaculatory ducts form where the vas deferens join with the ducts of the seminal vesicles in the prostate gland. They connect the vas deferens with the urethra. The ejaculatory ducts carry sperm from the vas deferens, 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 pH and provide nutrients to sperm, among other functions. The fluid itself provides sperm with a medium in which to “swim.”
Prostate Gland
The prostate gland 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 proteins, such as enzymes. In addition, it has a very high concentration of zinc, which is an important nutrient for maintaining sperm quality and motility.
Bulbourethral Glands
Also called Cowper’s glands, the two bulbourethral glands are 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 proteins. 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.
Figure 18.3.7 Male reproductive system.
Penis
The penis is 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.
Structure of the Penis
The 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.
Urethra
The urethra passes through the penis to carry urine from the bladder — or semen from the ejaculatory ducts — through the penis and out of the body. After leaving the urinary bladder, the urethra passes through the prostate gland, where the urethra is joined by the ejaculatory ducts. From there, the urethra passes through the penis 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.
Tissues of the Penis
The 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 foreskin, and below which is a layer of mucous membrane. The foreskin is attached to the penis at an area on the underside of the penis called the frenulum.
As 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 corpus cavernosum (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 urethra runs through this bottom column of spongy tissue, which is sometimes called corpus spongiosum. The glans penis also consists mostly of spongy erectile tissue. Veins and arteries run along the top of the penis, allowing blood circulation through the spongy tissues.
Feature: Human Biology in the News
Lung, heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when the nation’s first penis transplant took place, it was considered very newsworthy.
In 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. 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.
The 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world’s 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.
In 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.
18.3 Summary
- The two testes are sperm- and testosterone-producing male gonads. They are contained within the scrotum, a pouch that hangs down behind the penis. The testes are filled with hundreds of tiny, tightly coiled seminiferous tubules, where sperm are produced. The tubules contain sperm in different stages of development and also Sertoli cells, which secrete substances needed for sperm production. Between the tubules are Leydig cells, which secrete testosterone.
- Also contained within the scrotum are the two epididymes. Each epididymis is a tightly coiled tubule where sperm mature and are stored until they leave the body during an ejaculation.
- The two vas deferens are long, thin tubes that run from the scrotum up into the pelvic cavity. During ejaculation, each vas deferens carries sperm from one of the two epididymes to one of the pair of ejaculatory ducts.
- The two seminal vesicles are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. Semen contains alkaline substances and nutrients that sperm need to survive and “swim” in the female reproductive tract.
- The paired ejaculatory ducts form where the vas deferens joins with the ducts of the seminal vesicles in the prostate gland. They connect the vas deferens with the urethra. The ejaculatory ducts carry sperm from the vas deferens, as well as secretions from the seminal vesicles and prostate gland that together form semen.
- 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.
- The paired bulbourethral glands are located just below the prostate gland. They secrete a tiny amount of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic urine it may contain.
- 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 sexual intercourse so intromission can occur.
18.3 Review Questions
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- Describe the structure of a testis.
- Which parts of the male reproductive system are connected by the ejaculatory ducts? What fluids enter and leave the ejaculatory ducts?
- A vasectomy is a form of birth control for men that is performed by surgically cutting or blocking the vas deferens 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?
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18.3 Explore More
https://youtu.be/k60M1h-DKVY
Human Physiology - Functional Anatomy of the Male Reproductive System (Updated), Janux, 2015.
https://youtu.be/D1et5NgT6bQ
The Science of 'Morning Wood', AsapSCIENCE, 2012.
https://youtu.be/Ot7CYjm9B7U
I Had One Of The World's First Penis Transplants - Thomas Manning | This Morning, 2016.
Attributions
Figure 18.3.1
Lamb_fries by Paul Lowry on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 18.3.2
Human_reproductive_system_(Male) by Baresh25 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.3.3
Testicle by Unknown Illustrator from National Cancer Institute, of the National Institutes of Health, Visuals Online, ID 1769 is in the public domain (https://en.wikipedia.org/wiki/en:public_domain).
Figure 18.3.4
Testis-cross-section by Laura Guerin from CK-12 Foundation is used under a
CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
Figure 18.3.5
Epididymis-KDS by KDS444 on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.
Figure 18.3.6
3D_Medical_Animation_Vas_Deferens by https://www.scientificanimations.com/wiki-images (image 26 of 191) on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.3.7
Male anatomy blank [adapted] by Tsaitgaist on Wikimedia Commons is used and adapted by Christine Miller under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/) license. (Original: Male anatomy.png)
Figure 18.3.8
Penile-Clitoral_Structure by Esseh on Wikimedia Commons is used under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/) license.
Figure 18.3.9
Penis_cross_section.svg by Mcstrother on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
AsapSCIENCE, (2012, November 14). The science of 'morning wood'. YouTube. https://www.youtube.com/watch?v=D1et5NgT6bQ&feature=youtu.be
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
Brainard, J/ CK-12 Foundation. (2012). Figure 3 Cross section of a testis and seminiferous tubules [digital image]. In CK-12 Biology (Section 25.1) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-biology/section/25.1/
Gallagher, J. (2015, March 13). South Africans perform first 'successful' penis transplant (online article). BBC News. https://www.bbc.com/news/health-31876219
Grady, D. (2016, May 16). 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
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
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
Image shows a photomicrograph in which a stain has been applied that attached to only one specific type of cell.
Image shows a man jogging in the forest. His shirt is wet with sweat.
A molecule that can undergo polymerization, creating macromolecules. Large numbers of monomers combine to form polymers in a process called polymerization.
A sequence of nucleotides in DNA or RNA that codes for a molecule that has a function.
Case Study: Please Don’t Pass the Bread
Angela and Saloni are college students who met in physics class. They decide to study together for their upcoming midterm, but first, they want to grab some lunch. Angela says there is a particular restaurant she would like to go to, because they are able to accommodate her dietary restrictions. Saloni agrees and they head to the restaurant.
At lunch, Saloni asks Angela what is special about her diet. Angela tells her that she can’t eat gluten. Saloni says, “My cousin did that for a while because she heard that gluten is bad for you. But it was too hard for her to not eat bread and pasta, so she gave it up.” Angela tells Saloni that avoiding gluten isn’t optional for her — she has celiac disease. Eating even very small amounts of gluten could damage her digestive system. It can be difficult for people living with celiac disease to find foods when eating out.
You have probably heard of gluten, but what is it, and why is it harmful to people with celiac disease? Gluten is a protein present in wheat and some other grains (such as barley, rye, and oats), so it is commonly found in foods like bread, pasta, baked goods, and many packaged foods, like the ones pictured in Figure 15.1.2.
Figure 15.1.2 Gluten is a protein present in foods like bread, pasta, and baked goods.
For people with celiac disease, eating gluten causes an autoimmune reaction that results in damage to the small, finger-like villi lining the small intestine, causing them to become inflamed and flattened (see Figure 15.1.3). This damage interferes with the digestive process, which can result in a wide variety of symptoms including diarrhea, anemia, skin rash, bone pain, depression, and anxiety, among others. The degree of damage to the villi can vary from mild to severe, with more severe damage generally resulting in more significant symptoms and complications. Celiac disease can have serious long-term consequences, such as osteoporosis, problems in the nervous and reproductive systems, and the development of certain types of cancers.
Why does celiac disease cause so many different types of symptoms and have such significant negative health consequences? As you read this chapter and learn about how the digestive system works, you will see just how important the villi of the small intestine are to the body as a whole. At the end of the chapter, you will learn more about celiac disease, why it can be so serious, and whether it is worth avoiding gluten for people who do not have a diagnosed medical issue with it.
Chapter Overview: Digestive System
In this chapter, you will learn about the digestive system, which processes food so that our bodies can obtain nutrients. Specifically, you will learn about:
- The structures and organs of the gastrointestinal (GI) tract through which food directly passes. This includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
- The functions of the GI tract, including mechanical and chemical digestion, absorption of nutrients, and the elimination of solid waste.
- The accessory organs of digestion — the liver, gallbladder, and pancreas — which secrete substances needed for digestion into the GI tract, in addition to performing other important functions.
- Specializations of the tissues of the digestive system that allow it to carry out its functions.
- How different types of nutrients (such as carbohydrates, proteins, and fats) are digested and absorbed by the body.
- Beneficial bacteria that live in the GI tract and help us digest food, produce vitamins, and protect us from harmful pathogens and toxic substances.
- Disorders of the digestive system, including inflammatory bowel diseases, ulcers, diverticulitis, and gastroenteritis (commonly known as “stomach flu”).
As you read this chapter, think about the following questions related to celiac disease:
- What are the general functions of the small intestine? What do the villi in the small intestine do?
- Why do you think celiac disease causes so many different types of symptoms and potentially serious complications?
- What are some other autoimmune diseases that involve the body attacking its own digestive system?
Attributions
Figure 15.1.1
Bread [photo] by Sergio Arze on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 15.1.2
- Paste cu sos de roșii by Sestrjevitovschii Ina on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Cookies and More by Sarah Shaffer on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Raspberry waffles by Izabelle Acheson on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Homemade croissant & pain au chocolat by Cristiano Pinto on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 15.1.3
Inflammed_mucous_layer_of_the_intestinal_villi_depicting_Celiac_disease by www.scientificanimations.com (image 140/191) on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Image shows a photo of a woman doing a yoga pose which involves a backbend.
Created by CK-12/Adapted by Christine Miller
Looking at this photo of a football game (Figure 7.1.1), you can see why it is so important that the players wear helmets. As players tackle each other, football often involves forceful impact to the head. This can cause damage to the brain — temporarily (as in the case of a concussion) or long-term and more severe. Helmets are critical in reducing the incidence of traumatic brain injuries (TBIs), but they do not fully prevent them.
As a former professional football player who also played in college and high school, 43-year-old Jayson sustained many high-impact head injuries over the course of his football playing years. A few years ago, Jayson began experiencing a variety of troubling symptoms, including the loss of bladder control (the involuntary leakage of urine), memory loss, and difficulty walking. Symptoms like these are often signs of damage to the nervous system, which includes the brain, spinal cord, and nerves, but they can result from many different types of injuries or diseases that affect the nervous system. In order to treat him properly, Jayson’s doctors needed to do several tests to determine the exact cause of his symptoms. The doctors ordered a spinal tap to see if he had an infection, and an MRI (magnetic resonance imaging) to see if there were any observable problems in and around his brain.
The MRI revealed the cause of Jayson’s symptoms. There are fluid-filled spaces within the brain called ventricles, and compared to normal ventricles, Jayson’s ventricles were enlarged. Based on this observation, along with the results of other tests, Jayson’s doctor diagnosed him with hydrocephalus, a term that literally means “water head.” Hydrocephalus occurs when the fluid that fills the ventricles — called cerebrospinal fluid — builds up excessively, causing the ventricles to become enlarged. This puts pressure on the brain, which can cause a variety of neurological symptoms, including the ones Jayson was experiencing. In Figure 7.1.2, you can see the difference between normal ventricles and ventricles that are enlarged due to hydrocephalus. Notice in the image on the right how the brain becomes “squeezed” due to hydrocephalus.
Hydrocephalus often occurs at birth, as a result of genetic factors or events that occurred during fetal development. Because babies are born with skull bones that are not fully fused, the skull of a baby born with hydrocephalus can expand and relieve some of the pressure on the brain, as reflected in the enlarged head size shown in Figure 7.1.2. Adults have fully fused, inflexible skulls, so when hydrocephalus occurs in an adult, the brain experiences all of the increased pressure.
Why did Jayson develop hydrocephalus? There are many possible causes of hydrocephalus in adults, including tumors, infections, hemorrhages, and TBIs. Given his repeated and long history of football-related TBIs and the absence of any evidence of infection, tumor, or other cause, Jayson’s doctor thinks his head injuries were most likely responsible for his hydrocephalus.
Although hydrocephalus is serious, there are treatments. Read the rest of this chapter to learn about the cells, tissues, organs, cavities, and systems of the body, how they are interconnected, and the importance of keeping the body in a state of homeostasis (or balance). The amount of cerebrospinal fluid in the ventricles is normally kept at a relatively steady level, and the potentially devastating symptoms of hydrocephalus are an example of what can happen when a system in the body becomes unbalanced. At the end of the chapter, you will learn about Jayson’s treatment and prognosis.
Chapter Overview: Introduction to the Human Body
In this chapter, you will learn about the general organization and functions of the human body. Specifically, you will learn about:
- The organization of the body from atoms and molecules up through cells, tissues, organs, and organ systems.
- How organ systems work together to carry out the functions of life.
- The variety of different specialized cell types in humans, the four major types of human tissues, and some of their functions.
- The five vital organs and the 11 major organ systems of the human body.
- Spaces in the body called body cavities, and the organs they hold and protect.
- The tissues and fluid that protect the brain and spinal cord.
- How organ systems communicate and interact in body processes, such as cellular respiration, digestion, the fight-or-flight response to stressors, and physical activities (such as sports).
- How homeostasis is maintained to keep the body in a relatively steady state, and the problems that can be caused by loss of homeostasis, such as diabetes.
As you read the chapter, think about the following questions:
- What is the normal function of cerebrospinal fluid?
- What is a spinal tap and how does it test for infection?
- In Jayson’s case, what organs and organ systems are probably affected by his hydrocephalus? What are some ways in which these organ systems interact?
- The level of cerebrospinal fluid is normally kept in a state of homeostasis. What are other examples of types of homeostasis that keep your body functioning properly?
Attributions
Figure 7.1.1.
Football tackel [photo] by John Torcasio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 7.1.2
Hydrocephalus by Centers for Disease Control and Prevention (CDC) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Mayo Clinic Staff. (n.d.). Hydrocephalus [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/hydrocephalus/symptoms-causes/syc-20373604
Mayo Clinic Staff. (n.d.). Traumatic brain injury [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/traumatic-brain-injury/symptoms-causes/syc-20378557
Image shows a simple labelled diagram of a sperm. It contains a head (with nucleus and DNA), a midpeice which connects it to the flagellum, and a top portion on the head which contains enzymes.
Image shows a diagram of all the components of the endocrine system. This includes the pineal and pituitary glands in the brain, the thyroid gland surrounding the larynx, the thymus gland sitting above the heart, the adrenal glands sitting above the kidneys, the pancreas, and in females, the uterus and ovaries and in males the testes.
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