18.5 Disorders of the Male Reproductive System
Offering to the Gods
The marble and depicted in Figure 18.5.1 comes from ancient Rome, during the period from about 200 BCE to 400 CE. During that time, offerings like this were commonly given to the gods by people with health problems, either in the hopes of a cure, or as thanks for receiving one. The offerings were generally made in the shape of the afflicted body part. Scholars think this marble penis and scrotum may have been an offering given in hopes of — or thanks for — a cure for impotence, known medically today as erectile dysfunction.
Erectile Dysfunction
(ED) is sexual dysfunction characterized by the regular and repeated inability of a sexually mature male to obtain or maintain an . It is a common disorder that affects about 40% of males, at least occasionally.
Causes of Erectile Dysfunction
The normally stiffens and becomes erect when the columns of spongy tissue within the shaft of the penis (the and in Figure 18.5.2) become engorged with blood. Anything that hampers normal blood flow to the penis may therefore interfere with its potential to fill with blood and become erect. The normal nervous control of sexual arousal or penile engorgement may also fail and lead to problems obtaining or maintaining an erection.
Specific causes of ED include both physiological and psychological causes. Physiological causes include the use of therapeutic drugs (such as ), aging, , diseases (such as or ), tobacco smoking, and treatments for other disorders (such as prostate cancer). Psychological causes are less common, but may include stress, performance anxiety, or mental disorders. The risk of ED may also be greater in men with , , poor dietary habits, and overall poor physical health. Having an untreated hernia in the groin may also lead to ED.
Treatments for Erectile Dysfunction
Treatment of ED depends on its cause or contributing factors. For example, for tobacco smokers, smoking cessation may bring significant improvement in ED. Improving overall physical health by losing weight and exercising regularly may also be beneficial. The most common first-line treatment for ED, however, is the use of oral prescription drugs, known by brand names such as Viagra® and Cialis®. These drugs help ED by increasing blood flow to the . Other potential treatments include topical creams applied to the penis, injection of drugs into the penis, or the use of a vacuum pump that helps draw blood into the penis by applying negative pressure. More invasive approaches may be used as a last resort if other treatments fail. These usually involve surgery to implant inflatable tubes or rigid rods into the penis.
Ironically, the world’s most venomous spider —the Brazilian wandering spider (see Figure 18.5.3) — may offer a new treatment for ED. The venom of this spider is known to cause priapism in human males. Priapism is a prolonged erection that may damage the reproductive organs and lead to infertility if it continues too long. Researchers are investigating one of the components of the spider’s venom as a possible treatment for ED, if taken in minute quantities.
Epididymitis
is inflammation of the . The epididymis is one of the paired organs within the scrotum where mature and are stored. You can see its location in Figure 18.5.4. Discomfort or pain and swelling in the scrotum are typical symptoms of epididymitis, which is a relatively common condition, especially in young men.
Acute vs. Chronic Epididymitis
Epididymitis may be acute or chronic. Acute diseases are generally short-term conditions, whereas chronic diseases may last years — or even lifelong.
Acute Epididymitis
Acute epididymitis generally has a fairly rapid onset, and is most often caused by a bacterial infection. in the urethra can back-flow through the urinary and reproductive structures to the epididymis. In sexually active males, approximately 65% of cases of acute epididymitis are caused by sexually transmitted bacteria. Besides pain and swelling, common symptoms of acute epididymitis include redness and warmth in the scrotum, and a fever. There may also be a urethral discharge.
Chronic Epididymitis
Chronic epididymitis is epididymitis that lasts for more than three months. In some men, the condition may last for years. It may occur with or without a bacterial infection being diagnosed. Sometimes, it is associated with lower back pain that occurs after an activity that stresses the lower back, such as heavy lifting or a long period spent driving a vehicle.
Treatment of Epididymitis
If a bacterial infection is suspected, both acute and chronic epididymitis are generally treated with antibiotics. For chronic epididymitis, antibiotic treatment may be prescribed for as long as four to six weeks to ensure the complete eradication of any possible bacteria. Additional treatments often include anti-inflammatory drugs to reduce inflammation of the tissues, and painkillers to control the pain, which may be severe. Physically supporting the scrotum and applying cold compresses may also be recommended to help relieve swelling and pain.
Regardless of symptoms, treatment is important for both acute and chronic epididymitis, because major complications may occur otherwise. Untreated acute epididymitis may lead to an abscess — which is a buildup of pus — or to the infection spreading to other organs. Untreated chronic epididymitis may lead to permanent damage to the epididymis and testis, and it may even cause infertility.
Male Reproductive Cancers
Why does the airplane in Figure 18.5.5 have a huge mustache on its “face”? The mustache is a symbol of “Movember.” This is an international campaign to raise awareness of prostate cancer, as well as money to fund prostate cancer research.
Prostate Cancer
The is an organ located in the male pelvis (see Figure 18.5.6). The passes through the prostate gland after it leaves the bladder and before it reaches the . The function of the prostate is to secrete zinc and other substances into semen during an ejaculation. In Canada, is the most common type of cancer in men, and the second leading cause of male cancer death. About 1 in 9 Canadian men will be diagnosed with prostate cancer. Prostate cancer occurs at higher rates in rich nations like Canada and the United States, but the rates are increasing everywhere.
How Prostate Cancer Occurs
occurs when glandular cells of the prostate mutate into tumor cells. Eventually, the tumor, if undetected, may invade nearby structures, such as the . Tumor cells may also metastasize and travel in the bloodstream or to organs elsewhere in the body. Prostate cancer most commonly metastasizes to the s, s, , or lower urinary tract organs.
Symptoms of Prostate Cancer
Early in the course of prostate cancer, there may be no symptoms. When symptoms do occur, they mainly involve urination, because the urethra passes through the prostate gland. The symptoms typically include frequent urination, difficulty starting and maintaining a steady stream of , blood in the urine, and painful urination. Prostate cancer may also cause problems with sexual function, such as difficulty achieving erection or painful ejaculation.
Risk Factors for Prostate Cancer
Some factors that increase the risk of prostate cancer can be changed, and others cannot.
- Risk factors that can be changed include a diet high in meat, a sedentary lifestyle, , and high .
- Risk factors that cannot be changed include older age, a family history of prostate cancer, and African ancestry. Family history is an important risk factor, so are clearly involved. Many different genes have been implicated.
Diagnosing Prostate Cancer
The only definitive test to confirm a diagnosis of prostate cancer is a biopsy. In this procedure, a small piece of the prostate gland is surgically removed and then examined microscopically. A biopsy is done only after less invasive tests have found evidence that a patient may have prostate cancer.
A routine exam by a doctor may find a lump on the prostate, which might be followed by a blood test that detects an elevated level of prostate-specific antigen (PSA). PSA is a protein secreted by the prostate that normally circulates in the blood. Higher-than-normal levels of PSA can be caused by prostate cancer, but they may also have other causes. Ultrasound or magnetic resonance imaging (MRI) might also be undertaken to provide images of the prostate gland and additional information about the cancer.
Treatment of Prostate Cancer
The average age at which men are diagnosed with prostate cancer is 70 years. Prostate cancer typically is such a slow-growing cancer that elderly patients may not require treatment. Instead, the patients are watched carefully over the subsequent years to make sure the cancer isn’t growing and posing an immediate threat — an approach that is called active surveillance. It is used for at least 50% of patients who are expected to die from other causes before their prostate cancer causes symptoms.
Treatment of younger patients — or those with more aggressively growing tumors — may include surgery to remove the prostate,, and/or radiation therapy (such as brachytherapy, see Figure 18.5.7). All of these treatment options can have significant side effects, such as or urinary incontinence. Patients should learn the risks and benefits of the different treatments, and discuss them with their healthcare provider to decide on the best treatment options for their particular case.
Testicular Cancer
The reproductive cancer that most commonly affects young men is . The testes are the paired reproductive organs in the scrotum that produce and secrete . Although testicular cancer is rare, it is one of the few cancers that is more common in younger than older people. In fact, cancer of the testis is the most common cancer in males between the ages of 20 and 39 years. The risk of testicular cancer is about four to five times greater in men of European than African ancestry. The cause of this difference is unknown.
Signs and Symptoms of Testicular Cancer
One of the first signs of testicular cancer is often a lump or swelling in one of the two testes. The lump may or may not be painful. If pain is present, it may occur as a sharp pain or a dull ache in the lower abdomen or scrotum. Some men with testicular cancer report a feeling of heaviness in the scrotum. Testicular cancer does not commonly spread beyond the testis, but if it does, it most often spreads to the lungs, where it may cause shortness of breath or a cough.
Diagnosis of Testicular Cancer
The main way that testicular cancer is diagnosed is by detection of a lump in the testis. This is likely followed by further diagnostic tests. An ultrasound may be done to determine the exact location, size, and characteristics of the lump. Blood tests may be done to identify and measure tumor-marker proteins in the blood that are specific to testicular cancer. CT scans may also be done to determine whether the disease has spread beyond the testis. However, unlike the case with prostate cancer, a biopsy is not recommended, because it increases the risk of cancer cells spreading into the .
Treatment of Testicular Cancer
Testicular cancer has one of the highest cure rates of all cancers; it is estimated that 1 in every 250 men will develop this cancer in their lifetime. Three basic types of treatment for testicular cancer are surgery, radiation therapy, and/or chemotherapy. Generally, the initial treatment is surgery to remove the affected testis. If the cancer is caught at an early stage, the surgery is likely to cure the cancer, and has nearly a 100% five-year survival rate. When just one testis is removed, the remaining testis (if healthy) is adequate to maintain fertility, hormone production, and other normal male functions. Radiation therapy and/or chemotherapy may follow surgery to kill any tumor cells that might exist outside the affected testis, even when there is no indication that the cancer has spread. In many cases, however, surgery is followed by surveillance instead of additional treatments.
Feature: My Human Body
Testicular self-exams may catch testicular cancer at a relatively early stage, when a cure is most likely. The Testicular Cancer Foundation of Canada recommends monthly testicular self-exams for all male adolescents and young men. There is no medical consensus on testicular self-exams, however, and some medical organizations even recommend against them. The latter argue that the potential harms of self exams — which include false positive results, anxiety, and risks from diagnostic procedures — outweigh the potential benefits, given the very low incidence and high cure rate of even advanced testicular cancer. If you are a young male, you should discuss with your physician whether you should perform routine testicular self-exams. The self-exam is quick, easy, and painless to do. You can see how to perform a testicular self-exam by visiting the Testicular Canada Website. or watching the video “How to perform a testicular self exam from #TheRCT” below:
How to perform a testicular self exam from #TheRCT, The Robin Cancer Trust, 2013.
Regardless of whether you perform regular testicular self-exams, if you notice any of the following signs or symptoms, you should be examined by a doctor:
- A lump in one testis.
- A change in size of one testis.
- Pain or tenderness in the testis.
- Blood in the semen during ejaculation.
- Blood in the urine.
- Build-up of fluid in the scrotum.
18.5 Summary
- (ED) is a disorder characterized by the regular and repeated inability of a sexually mature male to obtain and maintain an . ED is a common disorder that occurs when normal blood flow to the penis is disturbed, or when there are problems with the nervous control of penile engorgement or arousal.
- Possible physiological causes of ED include aging, illness, drug use, tobacco smoking, and obesity, among others. Possible psychological causes of ED include stress, performance anxiety, and mental disorders.
- Treatments for ED may include lifestyle changes, such as stopping smoking, adopting a healthier diet, and regular exercise. The first-line treatment, however, is prescription drugs such as Viagra® or Cialis® that increase blood flow to the penis. Vacuum pumps or penile implants may be used to treat ED if other types of treatment fail.
- is inflammation of the . It is a common disorder, especially in young men. It may be acute or chronic, and is often caused by a bacterial infection. Treatments may include antibiotics, anti-inflammatory drugs, and painkillers. Treatment is important to prevent the possible spread of infection, permanent damage to the epididymis or testes, and even infertility.
- is the most common type of cancer in men, and the second leading cause of cancer death in men. If there are symptoms, they typically involve urination, such as frequent or painful urination. Risk factors for prostate cancer include older age, family history, high-meat diet, and sedentary lifestyle, among others.
- Prostate cancer may be detected by a physical exam or a high level of prostate-specific antigen (PSA) in the blood, but a biopsy is required for a definitive diagnosis. Prostate cancer is typically diagnosed relatively late in life and is usually slow growing, so treatment may not be necessary. In younger patients or those with faster-growing tumors, treatment is likely to include surgery to remove the prostate, followed by chemotherapy and/or radiation therapy.
- , or cancer of the testes, is the most common cancer in males between the ages of 20 and 39 years. It is more common in males of European than African ancestry. A lump or swelling in one testis, fluid in the scrotum, and testicular pain or tenderness are possible signs and symptoms of testicular cancer.
- Testicular cancer can be diagnosed by a physical exam and diagnostic tests, such as ultrasound or blood tests. Testicular cancer has one of the highest cure rates of all cancers. It is typically treated with surgery to remove the affected testis, and this may be followed by radiation therapy and/or chemotherapy. If the remaining testis is healthy, normal male reproductive functions are still possible after one testis is removed.
18.5 Review Questions
- Identify some of the underlying causes of erectile dysfunction. Discuss types of treatment for erectile dysfunction.
- Identify possible treatments for epididymitis. Why is treatment important, even when there are no symptoms?
- What are some of the symptoms of prostate cancer? List risk factors for prostate cancer. How is prostate cancer detected?
- In many cases, treatment for prostate cancer is unnecessary. Why? When is treatment necessary, and what are treatment options?
- Testicular cancer is generally rare, but it is the most common cancer in one age group. What age group is it?
- Identify possible signs and symptoms of testicular cancer. How can testicular cancer be diagnosed? Describe how testicular cancer is typically treated.
18.5 Explore More
Healthier men, one moustache at a time – Adam Garone, TED-Ed, 2013.
Can Spider Venom Cure Erectile Dysfunction? Gross Science, 2015.
Undescended Testes: Ask The Expert featuring Dr. Earl Cheng, Lurie Children’s, Ann & Robert H. Lurie Children’s Hospital of Chicago, 2012.
What Can Herpes Do To Your Brain? Gross Science, 2015.
Dangers of Herbal Viagra Exposed After Lamar Odom Reportedly Took Pills, Inside Edition, 2017.
Attributions
Figure 18.5.1
Votive_male_genitalia,_Roman,_200_BCE-400_CE_Wellcome_L0058590 by Wellcome Images on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.
Figure 18.5.2
Erection.svg by Hariadhi on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.5.3
Wandering spider by Andreas Kay on Flickr is used under a CC BY-NC-SA 2.0 (https://creativecommons.org/licenses/by-nc-sa/2.0/) license.
Figure 18.5.4
Male_reproductive_system unlabeled by Tsaitgaist (derivative work) on Wikimedia Commons is used under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/) license. (Original: Male anatomy.png)
Figure 18.5.5
Movember_(8140167077) by Eva Rinaldi on Wikimedia Commons is used under a CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0) license.
Figure 18.5.6
Prostatelead by National Cancer Institute on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:Public_domain).
Figure 18.5.7
Brachytherapybeads by James Heilman, MD on Wikimedia Commons CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
References
Ann & Robert H. Lurie Children’s Hospital of Chicago. (2012, December 21). Undescended testes: Ask the expert featuring Dr. Earl Cheng, Lurie Children’s. YouTube. https://www.youtube.com/watch?v=DuGXcEjDblI&feature=youtu.be
Gross Science. (2015, August 17). Can spider venom cure erectile dysfunction? YouTube. https://www.youtube.com/watch?v=5i9X8h17VNM&feature=youtu.be
Gross Science. (2015, May 27). What can herpes do to your brain? YouTube. https://www.youtube.com/watch?v=PEIVtXY39NM&feature=youtu.be
Inside Edition. (2017, ). Dangers of herbal viagra exposed after Lamar Odom reportedly took pills. YouTube. https://www.youtube.com/watch?v=ECx8YHo2f5c&feature=youtu.be
Self-examination guide. (n.d.). Testicular Cancer Canada. https://www.testicularcancer.ngo/selfexamination-guide
TED-Ed. (2013, April 7). Healthier men, one moustache at a time – Adam Garone. YouTube. https://www.youtube.com/watch?v=6D4Mmr2E7hM&feature=youtu.be
The Robin Cancer Trust. (2013, November 11). How to perform a testicular self exam from #TheRCT. YouTube. https://www.youtube.com/watch?v=NvDglB_HXyE&feature=youtu.be
Image shows a diagram of the heart with all chambers and major vessels labelled. Arrows indicate blood flow. Deoxygenated blood is brought the the right atrium by the superior and inferior vena cava. The right atrium moves blood into the right ventricle, which then sends blood to the lungs via the pulmonary arteries. Oxygenated blood returns to the heart from the lungs via the pulmonary veins and enters the left atrium. From there, blood is pumped into the left ventricle and then into the aorta for distribution to the body.
Image shows a female clinician dressed in scrubs listening to the heartbeat of a patient.
Created by CK-12 Foundation/Adapted by Christine Miller
Getting Rid of Wastes
The many chimneys on these houses are one way that the inhabitants of the home get rid of the wastes they produce. The chimneys expel waste gases that are created when they burn fuel in their furnace or fireplace. Think about the other wastes that people create in their homes and how we dispose of them. Solid trash and recyclables may go to the curb in a trash can, or in a recycling bin for pick up and transport to a landfill or recycling centre. Wastewater from sinks, showers, toilets, and the washing machine goes into a main sewer pipe and out of the house to join the community’s sanitary sewer system.
Like a busy home, your body also produces a lot of wastes that must be eliminated. Like a home, the way your body gets rid of wastes depends on the nature of the waste products. Some human body wastes are gases, some are solids, and some are in a liquid state. Getting rid of body wastes is called excretion, and there are a number of different organs of excretion in the human body.
Excretion
is the process of removing wastes and excess water from the body. It is an essential process in all living things, and it is one of the major ways the human body maintains . It also helps prevent damage to the body. Wastes include by-products of — some of which are toxic — and other non-useful materials, such as used up and broken down components. Some of the specific waste products that must be excreted from the body include carbon dioxide from , and from protein catabolism, and from nucleic acid catabolism.
Excretory Organs
Organs of excretion include the , , , , and (see Figure 16.2.2). Together, these organs make up the . They all excrete wastes, but they don’t work together in the same way that organs do in most other body systems. Each of the excretory organs “does its own thing” more-or-less independently of the others, but all are necessary to successfully excrete the full range of wastes from the human body.
Figure 16.2.2 Internal organs of excretion are identified in this illustration. They include the skin, liver, large intestine, lungs, and kidneys.
Skin
The is part of the integumentary system, but it also plays a role in excretion through the production of by sweat glands in the dermis. Although the main role of sweat production is to cool the body and maintain temperature , sweating also eliminates excess water and salts, as well as a small amount of urea. When sweating is copious, as in Figure 16.2.3, ingestion of salts and water may be helpful to maintain homeostasis in the body.
Liver
The liver (shown in Figure 16.2.4) has numerous major functions, including secreting for digestion of lipids, synthesizing many proteins and other compounds, storing glycogen and other substances, and secreting endocrine hormones. In addition to all of these functions, the liver is a very important organ of excretion. The liver breaks down many substances in the blood, including toxins. For example, the liver transforms — a poisonous by-product of protein — into , which is filtered from the blood by the kidneys and excreted in urine. The liver also excretes in its bile the protein , a byproduct of that forms when red blood cells die. Bile travels to the small intestine and is then excreted in by the .
Large Intestine
The is an important part of the digestive system and the final organ in the gastrointestinal tract. As an organ of excretion, its main function is to eliminate solid wastes that remain after the digestion of food and the extraction of water from indigestible matter in food waste. The large intestine also collects wastes from throughout the body. secreted into the gastrointestinal tract, for example, contains the waste product from the liver. Bilirubin is a brown pigment that gives human its characteristic brown colour.
Lungs
The lungs are part of the respiratory system (shown in Figure 16.2.5), but they are also important organs of excretion. They are responsible for the excretion of gaseous wastes from the body. The main waste gas excreted by the lungs is carbon dioxide, which is a waste product of in cells throughout the body. Carbon dioxide is diffused from the blood into the air in the tiny air sacs called in the lungs (shown in the inset diagram). By expelling carbon dioxide from the blood, the lungs help maintain acid-base . In fact, it is the pH of blood that controls the rate of breathing. Water vapor is also picked up from the lungs and other organs of the respiratory tract as the exhaled air passes over their moist linings, and the water vapor is excreted along with the carbon dioxide. Trace levels of some other waste gases are exhaled, as well.
Kidneys
The paired kidneys are often considered the main organs of excretion. The primary function of the kidneys is the elimination of excess water and wastes from the bloodstream by the production of the liquid waste known as . The main structural and functional units of the kidneys are tiny structures called nephrons. filter materials out of the blood, return to the blood what is needed, and excrete the rest as urine. As shown in Figure 16.2.6, the kidneys are organs of the urinary system, which also includes the ureters, bladder, and urethra — organs that transport, store, and eliminate urine, respectively.
By producing and excreting urine, the kidneys play vital roles in body-wide . They maintain the correct volume of extracellular fluid, which is all the fluid in the body outside of cells, including the blood and lymph. The kidneys also maintain the correct balance of salts and pH in extracellular fluid. In addition, the kidneys function as endocrine glands, secreting hormones into the blood that control other body processes. You can read much more about the kidneys in section 16.4 Kidneys.
16.2 Summary
- is the process of removing wastes and excess water from the body. It is an essential process in all living things and a major way the human body maintains .
- Organs of excretion include the skin, liver, large intestine, lungs, and kidneys. All of them excrete wastes, and together they make up the .
- The plays a role in excretion through the production of sweat by sweat glands. Sweating eliminates excess water and salts, as well as a small amount of , a byproduct of protein catabolism.
- The is a very important organ of excretion. The liver breaks down many substances in the blood, including toxins. The liver also excretes — a waste product of — in bile. Bile then travels to the , and is eventually excreted in by the .
- The main excretory function of the large intestine is to eliminate solid waste that remains after food is digested and water is extracted from the indigestible matter. The large intestine also collects and excretes wastes from throughout the body, including bilirubin in .
- The are responsible for the excretion of gaseous wastes, primarily carbon dioxide from in cells throughout the body. Exhaled air also contains water vapor and trace levels of some other waste gases.
- The paired are often considered the main organs of excretion. Their primary function is the elimination of excess water and wastes from the bloodstream by the production of urine. The kidneys contain tiny structures called that filter materials out of the blood, return to the blood what is needed, and excrete the rest as . The kidneys are part of the urinary system, which also includes the ureters, urinary bladder, and urethra.
16.2 Review Questions
- What is excretion, and what is its significance?
- Describe the excretory functions of the liver.
- What are the main excretory functions of the large intestine?
- List organs of the urinary system.
- Describe the physical states in which the wastes from the human body are excreted.
- Give one example of why ridding the body of excess water is important.
- What gives feces its brown colour? Why is that substance produced?
16.2 Explore More
https://www.youtube.com/watch?v=erMCADOJcHk&feature=youtu.be
Why Can We Regrow A Liver (But Not A Limb)? MITK12Videos, 2015.
https://www.youtube.com/watch?v=SeK0zFB9yHg&feature=youtu.be
Are Sports Drinks Good For You? | Fit or Fiction, POPSUGAR Fitness, 2014.
https://www.youtube.com/watch?v=fctH_1NuqCQ&feature=youtu.be
Why do we sweat? - John Murnan, TED-Ed, 2018.
Attributions
Figure 16.2.1
Chimneys/ Kingston upon Hull, England [photo] by Angela Baker on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 16.2.2
- Sweat or rain? by Kullez on Flickr is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/).
- Kidney front - white from www.medicalgraphics.de is used under a CC BY-ND 4.0 (https://creativecommons.org/licenses/by-nd/4.0/) license.
- File:Liver Cirrhosis.png by BruceBlaus on Wikimedia Commons is used under a CC BY SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
- File:Human lungs.png by Sharanyaudupa on Wikimedia Commons is used under a CC BY SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
- Tags: Offal Marking Medical Intestine Liver by Elionas2 on Pixabay is used under the Pixabay license (https://pixabay.com/service/license/).
Figure 16.2.3
gym_room_fitness_equipment_cardiovascular_exercise_elliptical_bike_cardio_training_sports_equipment_bodybuilding-825364 from Pxhere is used under a CC0 1.0 Universal public domain dedication license (https://creativecommons.org/publicdomain/zero/1.0/).
Figure 16.2.4
Tags: Liver Organ Anatomy by zachvanstone8 on Pixabay is used under the Pixabay License (https://pixabay.com/service/license/).
Figure 16.2.5
Lung_and_diaphragm by Terese Winslow/ National Cancer Institute on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 16.2.6
512px-Urinary_System_(Female) by BruceBlaus on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
References
MITK12Videos. (2015, June 4). Why can we regrow a liver (but not a limb)? https://www.youtube.com/watch?v=erMCADOJcHk&feature=youtu.be
POPSUGAR Fitness. (2014, February 7). Are sports drinks good for you? | Fit or Fiction. YouTube. https://www.youtube.com/watch?v=SeK0zFB9yHg&feature=youtu.be
TED-Ed. (2018, May 15). Why do we sweat? - John Murnan. YouTube. https://www.youtube.com/watch?v=fctH_1NuqCQ&feature=youtu.be
As per caption.
Created by CK-12 Foundation/Adapted by Christine Miller
Jaundiced Eyes
Did you ever hear of a person looking at something or someone with a “jaundiced eye”? It means to take a negative view, such as envy, maliciousness, or ill will. The expression may be based on the antiquated idea that liver bile is associated with such negative emotions as these, as well as the fact that excessive liver bile causes jaundice, or yellowing of the eyes and skin. Jaundice is likely a sign of a liver disorder or blockage of the duct that carries bile away from the liver. Bile contains waste products, making the liver an organ of excretion. Bile has an important role in digestion, which makes the liver an accessory organ of digestion, too.
What Are Accessory Organs of Digestion?
Accessory organs of digestion are organs that secrete substances needed for the chemical digestion of food, but through which food does not actually pass as it is digested. Besides the , the major accessory organs of digestion are the and . These organs secrete or store substances that are needed for digestion in the first part of the small intestine — the — where most chemical digestion takes place. You can see the three organs and their locations in Figure 15.6.2.
Liver
The is a vital organ located in the upper right part of the abdomen. It lies just below the , to the right of the . The liver plays an important role in digestion by secreting , but the liver has a wide range of additional functions unrelated to digestion. In fact, some estimates put the number of functions of the liver at about 500! A few of them are described below.
Structure of the Liver
The liver is a reddish brown, wedge-shaped structure. In adults, the liver normally weighs about 1.5 kg (about 3.3 lb). It is both the heaviest internal organ and the largest gland in the human body. The liver is divided into four lobes of unequal size and shape. Each lobe, in turn, is made up of lobules, which are the functional units of the liver. Each lobule consists of millions of liver cells, called hepatic cells (or hepatocytes). They are the basic metabolic cells that carry out the various functions of the liver.
As shown in Figure 15.6.3, the liver is connected to two large blood vessels: the hepatic artery and the portal vein. The hepatic artery carries oxygen-rich blood from the aorta, whereas the portal vein carries blood that is rich in digested nutrients from the GI tract and wastes filtered from the blood by the spleen. The blood vessels subdivide into smaller arteries and capillaries, which lead into the liver lobules. The nutrients from the GI tract are used to build many vital biochemical compounds, and the wastes from the spleen are degraded and excreted.
Functions of the Liver
The main digestive function of the liver is the production of bile. is a yellowish alkaline liquid that consists of water, electrolytes, bile salts, and cholesterol, among other substances, many of which are waste products. Some of the components of bile are synthesized by . The rest are extracted from the blood.
As shown in Figure 15.6.4, bile is secreted into small ducts that join together to form larger ducts, with just one large duct carrying bile out of the liver. If bile is needed to digest a meal, it goes directly to the duodenum through the common bile duct. In the duodenum, the bile neutralizes acidic chyme from the stomach and emulsifies fat globules into smaller particles (called micelles) that are easier to digest chemically by the enzyme lipase. Bile also aids with the absorption of vitamin K. Bile that is secreted when digestion is not taking place goes to the gallbladder for storage until the next meal. In either case, the bile enters the duodenum through the common bile duct.
Besides its roles in digestion, the liver has many other vital functions:
- The liver synthesizes glycogen from and stores the glycogen as required to help regulate blood sugar levels. It also breaks down the stored glycogen to glucose and releases it back into the blood as needed.
- The liver stores many substances in addition to glycogen, including vitamins A, D, B12, and K. It also stores the minerals iron and copper.
- The liver synthesizes numerous and many of the needed to make them. These proteins have a wide range of functions. They include fibrinogen, which is needed for blood clotting; insulin-like growth factor (IGF-1), which is important for childhood growth; and albumen, which is the most abundant protein in blood serum and functions to transport fatty acids and steroid hormones in the blood.
- The liver synthesizes many important lipids, including , triglycerides, and lipoproteins.
- The liver is responsible for the breakdown of many waste products and toxic substances. The wastes are excreted in bile or travel to the kidneys, which excrete them in urine.
The liver is clearly a vital organ that supports almost every other organ in the body. Because of its strategic location and diversity of functions, the liver is also prone to many diseases, some of which cause loss of liver function. There is currently no way to compensate for the absence of liver function in the long term, although liver dialysis techniques can be used in the short term. An artificial liver has not yet been developed, so liver transplantation may be the only option for people with liver failure.
Gallbladder
The is a small, hollow, pouch-like organ that lies just under the right side of the liver (see Figure 15.6.5). It is about 8 cm (about 3 in) long and shaped like a tapered sac, with the open end continuous with the cystic duct. The gallbladder stores and concentrates bile from the liver until it is needed in the duodenum to help digest lipids. After the bile leaves the liver, it reaches the gallbladder through the cystic duct. At any given time, the gallbladder may store between 30 to 60 mL (1 to 2 oz) of bile. A hormone stimulated by the presence of fat in the duodenum signals the gallbladder to contract and force its contents back through the cystic duct and into the common bile duct to drain into the duodenum.
Pancreas
The is a glandular organ that is part of both the and the . As shown in Figure 15.6.6, it is located in the abdomen behind the stomach, with the head of the pancreas surrounded by the duodenum of the small intestine. The pancreas is about 15 cm (almost 6 in) long, and it has two major ducts: the main pancreatic duct and the accessory pancreatic duct. Both of these ducts drain into the duodenum.
As an endocrine gland, the pancreas secretes several , including and , which circulate in the blood. The endocrine hormones are secreted by clusters of cells called pancreatic islets (or islets of Langerhans). As a digestive organ, the pancreas secretes many digestive enzymes and also bicarbonate, which helps neutralize acidic after it enters the . The pancreas is stimulated to secrete its digestive substances when food in the stomach and duodenum triggers the release of endocrine hormones into the blood that reach the pancreas via the bloodstream. The pancreatic digestive enzymes are secreted by clusters of cells called acini, and they travel through the pancreatic ducts to the duodenum. In the duodenum, they help to chemically break down carbohydrates, proteins, lipids, and nucleic acids in chyme. The pancreatic digestive enzymes include:
- , which helps digest starch and other carbohydrates.
- and , which help digest proteins.
- , which helps digest lipids.
- Deoxyribonucleases and ribonucleases, which help digest nucleic acids.
15.6 Summary
- Accessory organs of digestion are organs that secrete substances needed for the chemical digestion of food, but through which food does not actually pass as it is digested. The accessory organs include the liver, gallbladder, and pancreas. These organs secrete or store substances that are carried to the duodenum of the small intestine as needed for digestion.
- The is a large organ in the abdomen that is divided into lobes and smaller lobules, which consist of metabolic cells called hepatic cells, or . The liver receives oxygen in blood from the through the hepatic artery. It receives nutrients in blood from the GI tract and wastes in blood from the through the portal vein.
- The main digestive function of the liver is the production of the alkaline liquid called bile. is carried directly to the duodenum by the common bile duct or to the gallbladder first for storage. Bile neutralizes acidic that enters the duodenum from the stomach, and also emulsifies fat globules into smaller particles (micelles) that are easier to digest chemically.
- Other vital functions of the liver include regulating blood sugar levels by storing excess sugar as glycogen, storing many vitamins and minerals, synthesizing numerous proteins and lipids, and breaking down waste products and toxic substances.
- The is a small pouch-like organ near the liver. It stores and concentrates bile from the liver until it is needed in the duodenum to neutralize chyme and help digest lipids.
- The is a glandular organ that secretes both endocrine hormones and digestive enzymes. As an endocrine gland, the pancreas secretes insulin and glucagon to regulate blood sugar. As a digestive organ, the pancreas secretes digestive enzymes into the duodenum through ducts. Pancreatic digestive enzymes include amylase (starches) trypsin and chymotrypsin (proteins), lipase (lipids), and ribonucleases and deoxyribonucleases (RNA and DNA).
15.6 Review Questions
- Name three accessory organs of digestion. How do these organs differ from digestive organs that are part of the GI tract?
- Describe the liver and its blood supply.
- Explain the main digestive function of the liver and describe the components of bile and it's importance in the digestive process.
- What type of secretions does the pancreas release as part of each body system?
- List pancreatic enzymes that work in the duodenum, along with the substances they help digest.
- What are two substances produced by accessory organs of digestion that help neutralize chyme in the small intestine? Where are they produced?
- People who have their gallbladder removed sometimes have digestive problems after eating high-fat meals. Why do you think this happens?
- Which accessory organ of digestion synthesizes cholesterol?
15.6 Explore More
https://youtu.be/8dgoeYPoE-0
What does the pancreas do? - Emma Bryce, TED-Ed. 2015.
https://youtu.be/wbh3SjzydnQ
What does the liver do? - Emma Bryce, TED-Ed, 2014.
https://youtu.be/a0d1yvGcfzQ
Scar wars: Repairing the liver, nature video, 2018.
Attributions
Figure 15.6.1
Scleral_Icterus by Sheila J. Toro on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.
Figure 15.6.2
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.
Figure 15.6.3
Diagram_showing_the_two_lobes_of_the_liver_and_its_blood_supply_CRUK_376.svg by Cancer Research UK on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 15.6.4
Gallbladder by NIH Image Gallery on Flickr is used CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 15.6.5
Gallbladder_(organ) (1) by BruceBlaus on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license. (See a full animation of this medical topic at blausen.com.)
Figure 15.6.6
Blausen_0698_PancreasAnatomy 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.
nature video. (2018, December 19). Scar wars: Repairing the liver. YouTube. https://www.youtube.com/watch?v=a0d1yvGcfzQ&feature=youtu.be
TED-Ed. (2014, November 25). What does the liver do? - Emma Bryce. YouTube. https://www.youtube.com/watch?v=wbh3SjzydnQ&feature=youtu.be
TED-Ed. (2015, February 19). What does the pancreas do? - Emma Bryce. YouTube. https://www.youtube.com/watch?v=8dgoeYPoE-0&feature=youtu.be
Image shows a person's elbows with a rash that has caused redness and scabbing.
Image shows a detailed labelled diagram of a kidney. There is a tough outer layer called the capsule. The cortex contains blood vessels and the medulla contains nephrons. The renal artery brings blood from the heart to the kidney, and this blood is returned to the heart via the renal vein.
One Piano, Four Hands
Did you ever see two people play the same piano? How do they coordinate all the movements of their own fingers — let alone synchronize them with those of their partner? The peripheral nervous system plays an important part in this challenge.
What Is the Peripheral Nervous System?
The (PNS) consists of all the nervous tissue that lies outside of the (CNS). The main function of the PNS is to connect the CNS to the rest of the organism. It serves as a communication relay, going back and forth between the CNS and muscles, organs, and glands throughout the body.
Tissues of the Peripheral Nervous System
The PNS is mostly made up of cable-like bundles of axons called , as well as clusters of neuronal cell bodies called (singular, ). Nerves are generally classified as sensory, motor, or mixed nerves based on the direction in which they carry nerve impulses.
- Sensory nervesno post transmit information from sensory receptors in the body to the CNS. Sensory nerves are also called afferent nerves. You can see an example in the figure below.
- transmit information from the CNS to muscles, organs, and glands. Motor nerves are also called efferent nerves. You can see one in the figure below.
- contain both sensory and motor neurons, so they can transmit information in both directions. They have both afferent and efferent functions.
Divisions of the Peripheral Nervous System
The PNS is divided into two major systems, called the and the . In the diagram below, the autonomic system is shown on the left, and the somatic system on the right. Both systems of the PNS interact with the CNS and include sensory and motor neurons, but they use different circuits of nerves and ganglia.
Somatic Nervous System
The primarily senses the external environment and controls voluntary activities about which decisions and commands come from the cerebral cortex of the brain. When you feel too warm, for example, you decide to turn on the air conditioner. As you walk across the room to the thermostat, you are using your somatic nervous system. In general, the somatic nervous system is responsible for all of your conscious perceptions of the outside world, as well as all of the voluntary motor activities you perform in response. Whether it’s playing a piano, driving a car, or playing basketball, you can thank your somatic nervous system for making it possible.
Somatic sensory and motor information is transmitted through 12 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial nerves are in the head and neck and connect directly to the brain. Sensory components of cranial nerves transmit information about smells, tastes, light, sounds, and body position. Motor components of cranial nerves control skeletal muscles of the face, tongue, eyeballs, throat, head, and shoulders. Motor components of cranial nerves also control the salivary glands and swallowing. Four of the 12 cranial nerves participate in both sensory and motor functions as mixed nerves, having both sensory and motor neurons.
Spinal nerves emanate from the spinal column between vertebrae. All of the spinal nerves are mixed nerves, containing both sensory and motor neurons. The areas of skin innervated by the 31 pairs of spinal nerves are shown in the figure below. These include sensory nerves in the skin that sense pressure, temperature, vibrations, and pain. Other sensory nerves are in the muscles, and they sense stretching and tension. Spinal nerves also include motor nerves that stimulate skeletal muscles to contract, allowing for voluntary body movements.
Autonomic Nervous System
The primarily senses the internal environment and controls involuntary activities. It is responsible for monitoring conditions in the internal environment and bringing about appropriate changes in them. In general, the autonomic nervous system is responsible for all the activities that go on inside your body without your conscious awareness or voluntary participation.
Structurally, the autonomic nervous system consists of sensory and motor nerves that run between the CNS (especially the hypothalamus in the brain), internal organs (such as the heart, lungs, and digestive organs), and glands (such as the pancreas and sweat glands). in the autonomic system detect internal body conditions and send messages to the brain. Motor nerves in the autonomic system affect appropriate responses by controlling contractions of smooth or cardiac muscle, or glandular tissue. For example, when sensory nerves of the autonomic system detect a rise in body temperature, motor nerves signal smooth muscles in blood vessels near the body surface to undergo vasodilation, and the sweat glands in the skin to secrete more sweat to cool the body.
The autonomic nervous system, in turn, has three subdivisions: the , , and . The first two subdivisions of the autonomic system are summarized in the figure below. Both affect the same organs and glands, but they generally do so in opposite ways.
- The sympathetic division controls the fight-or-flight response. Changes occur in organs and glands throughout the body that prepare the body to fight or flee in response to a perceived danger. For example, the heart rate speeds up, air passages in the lungs become wider, more blood flows to the skeletal muscles, and the digestive system temporarily shuts down.
- The parasympathetic division returns the body to normal after the fight-or-flight response has occurred. For example, it slows down the heart rate, narrows air passages in the lungs, reduces blood flow to the skeletal muscles, and stimulates the digestive system to start working again. The parasympathetic division also maintains internal homeostasis of the body at other times.
- The enteric division is made up of nerve fibres that supply the organs of the digestive system. This division allows for the local control of many digestive functions.
Disorders of the Peripheral Nervous System
Unlike the CNS — which is protected by s, , and — the PNS has no such protections. The PNS also has no blood-brain barrier to protect it from toxins and pathogens in the blood. Therefore, the PNS is more subject to injury and disease than is the CNS. Causes of nerve injury include diabetes, infectious diseases (such as shingles), and poisoning by toxins (such as heavy metals). PNS disorders often have symptoms like loss of feeling, tingling, burning sensations, or muscle weakness. If a traumatic injury results in a nerve being transected (cut all the way through), it may regenerate, but this is a very slow process and may take many months.
Two other diseases of the PNS are Guillain-Barre syndrome and Charcot-Marie-Tooth disease.
- Guillain-Barre syndrome is a rare disease in which the immune system attacks nerves of the PNS, leading to muscle weakness and even paralysis. The exact cause of Guillain-Barre syndrome is unknown, but it often occurs after a viral or bacterial infection. There is no known cure for the syndrome, but most people eventually make a full recovery. Recovery can be slow, however, lasting anywhere from several weeks to several years.
- Charcot-Marie-Tooth disease is a hereditary disorder of the nerves, and one of the most common inherited neurological disorders. It affects predominantly the nerves in the feet and legs, and often in the hands and arms, as well. The disease is characterized by loss of muscle tissue and sense of touch. It is presently incurable.
Feature: My Human Body
The autonomic nervous system is considered to be involuntary because it doesn't require conscious input. However, it is possible to exert some voluntary control over it. People who practice yoga or other so-called mind-body techniques, for example, can reduce their heart rate and certain other autonomic functions. Slowing down these otherwise involuntary responses is a good way to relieve stress and reduce the wear-and-tear that stress can place on the body. Such techniques may also be useful for controlling post-traumatic stress disorder and chronic pain. Three types of integrative practices for these purposes are breathing exercises, body-based tension modulation exercises, and mindfulness techniques.
Breathing exercises can help control the rapid, shallow breathing that often occurs when you are anxious or under stress. These exercises can be learned quickly, and they provide immediate feelings of relief. Specific breathing exercises include paced breath, diaphragmatic breathing, and Breathe2Relax or Chill Zone on MindShift™ CBT, which are downloadable breathing practice mobile applications, or "Apps". Try syncing your breathing with Eric Klassen's "Triangle breathing, 1 minute" video:
https://www.youtube.com/watch?v=u9Q8D6n-3qw
Triangle breathing, 1 minute, Erin Klassen, 2015.
Body-based tension modulation exercises include yoga postures (also known as “asanas”) and tension manipulation exercises. The latter include the Trauma/Tension Release Exercise (TRE) and the Trauma Resiliency Model (TRM). Watch this video for a brief — but informative — introduction to the TRE program:
https://www.youtube.com/watch?v=67R974D8swM&feature=youtu.be
TRE® : Tension and Trauma Releasing Exercises, an Introduction with Jessica Schaffer, Jessica Schaffer Nervous System RESET, 2015.
Mindfulness techniques have been shown to reduce symptoms of depression, as well as those of anxiety and stress. They have also been shown to be useful for pain management and performance enhancement. Specific mindfulness programs include Mindfulness Based Stress Reduction (MBSR) and Mindfulness Mind-Fitness Training (MMFT). You can learn more about MBSR by watching the video below.
https://www.youtube.com/watch?v=0TA7P-iCCcY&feature=youtu.be
Mindfulness-Based Stress Reduction (UMass Medical School, Center for Mindfulness), Palouse Mindfulness, 2017.
8.6 Summary
- The (PNS) consists of all the nervous tissue that lies outside the (CNS). Its main function is to connect the CNS to the rest of the organism.
- The PNS is made up of and . Nerves are bundles of , and ganglia are groups of . Nerves are classified as sensory, motor, or a mix of the two.
- The PNS is divided into the and . The somatic system controls activities, whereas the autonomic system controls activities.
- The autonomic nervous system is further divided into , , and . The sympathetic division controls during emergencies, the parasympathetic system controls routine body functions the rest of the time, and the enteric division provides local control over the .
- The PNS is not as well protected physically or chemically as the CNS, so it is more prone to injury and disease. PNS problems include injury from diabetes, shingles, and heavy metal poisoning. Two disorders of the PNS are Guillain-Barre syndrome and Charcot-Marie-Tooth disease.
8.6 Review Questions
- Describe the general structure of the peripheral nervous system. State its primary function.
- What are ganglia?
- Identify three types of nerves based on the direction in which they carry nerve impulses.
- Outline all of the divisions of the peripheral nervous system.
- Compare and contrast the somatic and autonomic nervous systems.
- When and how does the sympathetic division of the autonomic nervous system affect the body?
- What is the function of the parasympathetic division of the autonomic nervous system? Specifically, how does it affect the body?
- Name and describe two peripheral nervous system disorders.
- Give one example of how the CNS interacts with the PNS to control a function in the body.
- For each of the following types of information, identify whether the neuron carrying it is sensory or motor, and whether it is most likely in the somatic or autonomic nervous system:
- Visual information
- Blood pressure information
- Information that causes muscle contraction in digestive organs after eating
- Information that causes muscle contraction in skeletal muscles based on the person’s decision to make a movement
8.6 Explore More
https://www.youtube.com/watch?v=ySIDMU2cy0Y&feature=emb_logo
Phantom Limbs Explained, Plethrons, 2015.
https://www.youtube.com/watch?time_continue=1&v=73yo5nJne6c&feature=emb_logo
Why Do Hot Peppers Cause Pain? Reactions, 2015.
Attributions
Figure 8.6.1
Kid’s piant duet by PJMixer on Flickr is used under a CC BY-NC-ND 2.0 (https://creativecommons.org/licenses/by-nc-nd/2.0/) license.
Figure 8.6.2
Nervous_system_diagram by ¤~Persian Poet Gal on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 8.6.3
Afferent_and_efferent_neurons_en.svg by Helixitta on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 8.6.4
Autonomic and Somatic Nervous System by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 8.6.5
Dermatoms.svg by Ralf Stephan (mailto:ralf@ark.in-berlin.de) on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 8.6.6
The_Autonomic_Nervous_System by Geo-Science-International on Wikimedia Commons is used and adapted by Christine Miller under a CC0 1.0 Universal
Public Domain Dedication license (https://creativecommons.org/publicdomain/zero/1.0/).
References
Erin Klassen. (2015, December 15). Triangle breathing, 1 minute. YouTube. https://www.youtube.com/watch?v=u9Q8D6n-3qw&feature=youtu.be
Jessica Schaffer Nervous System RESET. (2015, January 15). TRE® : Tension and trauma releasing exercises, an Introduction with Jessica Schaffer. YouTube. https://www.youtube.com/watch?v=67R974D8swM&feature=youtu.be
Mayo Clinic Staff. (n.d.). Charcot-Marie-Tooth disease [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/charcot-marie-tooth-disease/symptoms-causes/syc-20350517
Mayo Clinic Staff. (n.d.). Diabetes [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/diabetes/symptoms-causes/syc-20371444
Mayo Clinic Staff. (n.d.). Guillain-Barre syndrome [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/guillain-barre-syndrome/symptoms-causes/syc-20362793
Mayo Clinic Staff. (n.d.). Shingles [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/shingles/symptoms-causes/syc-20353054
Mayo Clinic Staff. (n.d.). Stroke [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/stroke/symptoms-causes/syc-20350113
Palouse Mindfulness. (2017, March 25). Mindfulness-based stress reduction (UMass Medical School, Center for Mindfulness), YouTube. https://www.youtube.com/watch?v=0TA7P-iCCcY&feature=youtu.be
Plethrons, (2015, March 23). Phantom limbs explained. YouTube. https://www.youtube.com/watch?v=ySIDMU2cy0Y&feature=youtu.be
Reactions. (2015, December 1). Why do hot peppers cause pain? YouTube. https://www.youtube.com/watch?v=73yo5nJne6c&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Fashion Statement
This colourful hairstyle makes quite a fashion statement. Many people spend a lot of time and money on their hair, even if they don’t have an exceptional hairstyle like this one. Besides its display value, hair actually has important physiological functions.
What is Hair?
is a filament that grows from a in the of the skin. It consists mainly of tightly packed, keratin-filled cells called . The human body is covered with hair follicles, with the exception of a few areas, including the mucous membranes, lips, palms of the hands, and soles of the feet.
Structure of Hair
The part of the hair located within the follicle is called the . The root is the only living part of the hair. The part of the hair that is visible above the surface of the skin is the hair shaft. The shaft of the hair has no biochemical activity and is considered dead.
Follicle and Root
Hair growth begins inside a follicle (see Figure 10.5.2 below). Each hair follicle contains stem cells that can keep dividing, which allows hair to grow. The stem cells can also regrow a new hair after one falls out. Another structure associated with a hair follicle is a sebaceous gland that produces oily sebum. The sebum lubricates and helps to waterproof the hair. A tiny arrector pili muscle is also attached to the follicle. When it contracts, the follicle moves, and the hair in the follicle stands up.
Shaft
The is a hard filament that may grow very long. Hair normally grows in length by about half an inch a month. In cross-section, a hair shaft can be divided into three zones, called the cuticle, cortex, and medulla.
- The (or outer coat) is the outermost zone of the hair shaft. It consists of several layers of flat, thin keratinocytes that overlap one another like shingles on a roof. This arrangement helps the cuticle repel water. The cuticle is also covered with a layer of lipids, just one molecule thick, which increases its ability to repel water. This is the zone of the hair shaft that is visible to the eye.
- The is the middle zone of the hair shaft, and it is also the widest part. The cortex is highly structured and organized, consisting of keratin bundles in rod-like structures. These structures give hair its mechanical strength. The cortex also contains melanin, which gives hair its colour.
- The is the innermost zone of the hair shaft. This is a small, disorganized, and more open area at the center of the hair shaft. The medulla is not always present. When it is present, it contains highly pigmented cells full of keratin.
Characteristics of Hair
Two visible characteristics of hair are its colour and texture. In adult males, the extent of balding is another visible characteristic. All three characteristics are genetically controlled.
Hair Colour
All natural hair colours are the result of , which is produced in hair follicles and packed into granules in the hair. Two forms of melanin are found in human hair: eumelanin and pheomelanin. is the dominant pigment in brown hair and black hair, and is the dominant pigment in red hair. Blond hair results when you have only a small amount of melanin in the hair. Gray and white hair occur when melanin production slows down, and eventually stops.
Figure 10.5.3 Variation in hair colouration. Which types of melanin are present for each hair colour shown?
Hair Texture
Hair exists in a variety of textures. The main aspects of hair texture are the curl pattern, thickness, and consistency.
- The shape of the determines the shape of the hair shaft. The shape of the , in turn, determines the curl pattern of the hair. Round hair shafts produce straight hair. Hair shafts that are oval or have other shapes produce wavy or curly hair .
- The size of the hair follicle determines the thickness of hair. Thicker hair has greater volume than thinner hair.
- The consistency of hair is determined by the hair follicle volume and the condition of the hair shaft. The consistency of hair is generally classified as fine, medium, or coarse. Fine hair has the smallest circumference, and coarse hair has the largest circumference. Medium hair falls in between these two extremes. Coarse hair also has a more open cuticle than thin or medium hair does, which causes it to be more porous.
Functions of Hair
In humans, one function of head hair is to provide insulation and help the head retain heat. Head hair also protects the skin on the head from damage by .
The function of hair in other locations on the body is debated. One idea is that body hair helps keep us warm in cold weather. When the body is too cold, muscles contract and cause hairs to stand up (shown in Figure 10.5.5), trapping a layer of warm air above the epidermis. However, this is more effective in mammals that have thick hair or fur than it is in relatively hairless human beings.
Human hair has an important sensory function, as well. Sensory receptors in the hair follicles can sense when the hair moves, whether it moves because of a breeze, or because of the touch of a physical object. The receptors may also provide sensory awareness of the presence of parasites on the skin.
Some hairs, such as the , are especially sensitive to the presence of potentially harmful matter. The eyelashes grow at the edge of the eyelid and can sense when dirt, dust, or another potentially harmful object is too close to the eye. The eye reflexively closes as a result of this sensation. The also provide some protection to the eyes. They protect the eyes from dirt, sweat, and rain. In addition, the eyebrows play a key role in nonverbal communication (see Figure 10.5.6). They help express emotions such as sadness, anger, surprise, and excitement.
Hair in Human Evolution
Among mammals, humans are nearly unique in having undergone significant loss of body hair during their evolution. Humans are also unlike most other mammals in having curly hair as one variation in hair texture. Even non-human primates (see Figure 10.5.7) all have straight hair. This suggests that curly hair evolved at some point during human evolution.
Loss of Body Hair
One for the loss of body hair in the human lineage is that it would have facilitated cooling of the body by the evaporation of sweat. Humans also evolved far more than other mammals, which is consistent with this hypothesis, because sweat evaporates more quickly from less hairy skin. Another hypothesis for human hair loss is that it would have led to fewer parasites on the skin. This might have been especially important when humans started living together in larger, more crowded social groups.
These hypotheses may explain why we lost body hair, but they can’t explain why we didn’t also lose head hair and hair in the pubic region and armpits. It is possible that head hair was retained because it protected the scalp from . As our bipedal ancestors walked on the open savannas of equatorial Africa, the skin on the head would have been an area exposed to the most direct rays of sunlight in an upright hominid. Pubic and armpit hair may have been retained because they served as signs of sexual maturity, which would have been important for successful mating and reproduction.
Evolution of Curly Hair
Greater protection from UV light has also been posited as a possible selective agent favoring the evolution of curly hair. Researchers have found that straight hair allows more light to pass into the body through the hair shaft via the follicle than does curly hair. In this way, human hair is like a fibre optic cable. It allows light to pass through easily when it is straight, but it impedes the passage of light when it is kinked or coiled. This is indirect evidence that UV light may have been a selective agent leading to the evolution of curly hair.
Social and Cultural Significance of Hair
Hair has great social significance for human beings. Body hair is an indicator of biological sex, because hair distribution is . Adult males are generally hairier than adult females, and facial hair in particular is a notable secondary male sex characteristic. Hair may also be an indicator of age. White hair is a sign of older age in both males and females, and male pattern baldness is a sign of older age in males. In addition, hair colour and texture can be a sign of ethnic ancestry.
Hair also has great cultural significance. Hairstyle and colour may be an indicator of social group membership and for better or worse can be associated with specific stereotypes. Head shaving has been used in many times and places as a punishment, especially for women. On the other hand, in some cultures, cutting off one’s hair symbolizes liberation from one’s past. In other cultures, it is a sign of mourning. There are also many religious-based practices involving hair. For example, the majority of Muslim women hide their hair with a headscarf. Sikh men grow their hair long and cover it with a turban. Amish men (like the one pictured in Figure 10.5.8) grow facial hair only after they marry — but just a beard, and not a mustache.
Unfortunately, sometimes hairstyle, colour and characteristics are used to apply stereotypes, particularly with respect to women. "Blonde jokes" are a good example of how negative stereotypes are maintained despite having no actual truth behind them. Many stereotypes related to hair are hidden, even from persons perpetrating the stereotype. Often a hairstyle is judged by another as having ties to gender, sexuality, worldview and/or socioeconomic status; even when these inferences are woefully inaccurate. It is important to be aware of our own biases and determine if these biases are appropriate - take a look at the collage in Figure 10.5.9. What are your initial reactions? Are these reactions founded in fact? Do you harbor an unfair bias?
Figure 10.5.9 What are your biases? Are they fair?
10.5 Summary
- Hair is a filament that grows from a in the of the skin. It consists mainly of tightly packed, keratin-filled cells called . The human body is almost completely covered with hair follicles.
- The part of a hair that is within the follicle is the . This is the only living part of a hair. The part of a hair that is visible above the skin surface is the . It consists of dead cells.
- Hair growth begins inside a follicle when stem cells within the follicle divide to produce new keratinocytes. An individual hair may grow to be very long.
- A hair shaft has three zones: the outermost zone called the ; the middle zone called the ; and the innermost zone called the .
- Genetically controlled, visible characteristics of hair include hair colour, hair texture, and the extent of balding in adult males. ( and/or ) is the pigment that gives hair its colour. Aspects of hair texture include curl pattern, thickness, and consistency.
- Functions of head hair include providing insulation and protecting skin on the head from . Hair everywhere on the body has an important sensory function. Hair in and protects the eyes from dust, dirt, sweat, and other potentially harmful substances. The eyebrows also play a role in nonverbal communication.
- Among mammals, humans are nearly unique in having undergone significant loss of body hair during their evolution, probably because sweat evaporates more quickly from less hairy skin. Curly hair also is thought to have evolved at some point during human evolution, perhaps because it provided better protection from UV light.
- Hair has social significance for human beings, because it is an indicator of biological sex, age, and ethnic ancestry. Human hair also has cultural significance. Hairstyle may be an indicator of social group membership, for example.
10.5 Review Questions
-
- Compare and contrast the hair root and hair shaft.
- Describe hair follicles.
- Explain variation in human hair colour.
- What factors determine the texture of hair?
- Describe two functions of human hair.
- What hypotheses have been proposed for the loss of body hair during human evolution?
- Discuss the social and cultural significance of human hair.
- Describe one way in which hair can be used as a method of communication in humans.
- Explain why waxing or tweezing body hair, which typically removes hair down to the root, generally keeps the skin hair-free for a longer period of time than shaving, which cuts hair off at the surface of the skin.
10.5 Explore More
https://www.youtube.com/watch?v=8diYLhl8bWU
Why do some people go bald? - Sarthak Sinha, TED-Ed, 2015.
https://www.youtube.com/watch?v=kNw8V_Fkw28
Hair Love | Oscar®-Winning Short Film (Full) | Sony Pictures Animation, 2019.
https://www.youtube.com/watch?v=hDW5e3NR1Cw
Why do we care about hair | Naomi Abigail | TEDxBaDinh, TEDx Talks, 2015.
Attributions
Figure 10.5.1
Hair by jessica-dabrowski-TETR8YLSqt4 [photo] by Jessica Dabrowski on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 10.5.2
Blausen_0438_HairFollicleAnatomy_02 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 10.5.3
- Standing tall by Ilaya Raja on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Blond-haired woman smiling by Carlos Lindner on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Smith Mountain Lake redhead by Chris Ross Harris on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Through the look of experience by Laura Margarita Cedeño Peralta on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 10.5.4
Curly hair by chris-benson-clvEami9RN4 [photo] by Chris Benson on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 10.5.5
1024px-PilioerectionAnimation by AnthonyCaccese on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 10.5.6
Pout by alexander-dummer-Em8I8Z_DwA4 [photo] by Alexander Dummer on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 10.5.7
Cotton_top_tamarin_monkey._(12046035746) by Bernard Spragg. NZ, from Christchurch, New Zealand on Wikimedia Commons is used under a CC0 1.0 Universal
Public Domain Dedication license (https://creativecommons.org/publicdomain/zero/1.0/deed.en).
Figure 10.5.8
Amish hairstyle by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
©CK-12 Foundation Licensed under • Terms of Use • Attribution
Figure 10.5.9
- Rainbow Hair Bubble Man by Behrouz Jafarnezhad on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Pink hair in Atlanta, United States by Tammie Allen on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Magdalena 2 by Valerie Elash on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Perfect Style by Daria Volkova on Unsplash is used under the Unsplash License (https://unsplash.com/license)
- Stay Classy by Fayiz Musthafa on Unsplash is used under the Unsplash License (https://unsplash.com/license)
- Take your time by Jan Tinneberg on Unsplash is used under the Unsplash License (https://unsplash.com/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 7 This style of facial hair is adopted by most Amish men after they marry [digital image]. In CK-12 College Human Biology (Section 12.5) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/12.5/
Sony Pictures Animation. (2019, December 5). Hair love | Oscar®-winning short film (Full) | Sony Pictures Animation. YouTube. https://www.youtube.com/watch?v=kNw8V_Fkw28
TED-Ed. (2015, August 25). Why do some people go bald? – Sarthak Sinha. YouTube. https://www.youtube.com/watch?v=8diYLhl8bWU
TEDx Talks. (2015, February 4). Why do we care about hair | Naomi Abigail | TEDxBaDinh. YouTube. https://www.youtube.com/watch?v=hDW5e3NR1Cw
Image shows three competing rowing teams in the 2016 Rio Summer Olympics. Each rowboat holds two women. In the photo are Canada, France and China.
Created by CK12/Adapted by Christine Miller
Jasmin discovered that her extreme fatigue, muscle pain, vision problems, and vomiting were due to problems in her , like the damaged shown in red in Figure 4.14.1. Mitochondria are small, membrane-bound organelles found in cells that provide energy for the cells of the body. They do this by carrying out the final two steps of aerobic cellular respiration: the and . This is the major way that the human body breaks down the sugar glucose from food into a form of energy cells can use, namely the molecule .
Because mitochondria provide energy for cells, you can understand why Jasmin was experiencing extreme fatigue, particularly after running. Her damaged mitochondria could not keep up with her need for energy, particularly after intense exercise, which requires a lot of additional energy. What is perhaps not so obvious are the reasons for her other symptoms, such as blurry vision, muscle spasms, and vomiting. All of the cells in the body require energy in order to function properly. Mitochondrial diseases can cause problems in mitochondria in any cell of the body, including muscle cells and cells of the nervous system, which includes the brain and nerves. The nervous system and muscles work together to control vision and digestive system functions, such as vomiting, so when they are not functioning properly, a variety of symptoms can emerge. This also explains why Jasmin’s niece, who has a similar mitochondrial disease, has symptoms related to brain function, such as seizures and learning disabilities. Our cells are microscopic, and mitochondria are even tinier — but they are essential for the proper functioning of our bodies. When they are damaged, serious health effects can occur.
One seemingly confusing aspect of mitochondrial diseases is that the type of symptoms, severity of symptoms, and age of onset can vary wildly between people — even within the same family! In Jasmin’s case, she did not notice symptoms until adulthood, while her niece had more severe symptoms starting at a much younger age. This makes sense when you know more about how mitochondrial diseases work.
Inherited mitochondrial diseases can be due to damage in either the in the nucleus of cells or in the DNA in the mitochondria themselves. Recall that mitochondria are thought to have evolved from prokaryotic organisms that were once free-living, but were then infected or engulfed by larger cells. One of the pieces of evidence that supports this is that mitochondria have their own, separate DNA. When the mitochondrial DNA is damaged (or mutated) it can result in some types of mitochondrial diseases. However, these mutations do not typically affect all of the mitochondria in a cell. During cell division, organelles such as mitochondria are replicated and passed down to the new daughter cells. If some of the mitochondria are damaged, and others are not, the daughter cells can have different amounts of damaged mitochondria. This helps explain the wide range of symptoms in people with mitochondrial diseases — even ones in the same family — because different cells in their bodies are affected in varying degrees. Jasmin’s niece was affected strongly and her symptoms were noticed early, while Jasmin’s symptoms were more mild and did not become apparent until adulthood.
There is still much more that needs to be discovered about the different types of mitochondrial diseases. But by learning about cells, their organelles, how they obtain energy, and how they divide, you should now have a better understanding of the biology behind these diseases.
Apply your understanding of cells to your own life. Can you think of other diseases that affect cellular structures or functions. Do they affect people you know? Since your entire body is made of cells, when cells are damaged or not functioning properly, it can cause a wide variety of health problems.
Chapter 4 Summary
Type your learning objectives here.
In this chapter you learned many facts about cells. Specifically, you learned that:
- Cells are the basic units of structure and function of living things.
- The first cells were observed from cork by Hooke in the 1600s. Soon after, van Leeuwenhoek observed other living cells.
- In the early 1800s, Schwann and Schleiden theorized that cells are the basic building blocks of all living things. Around 1850, Virchow saw cells dividing, and added his own theory that living cells arise only from other living cells. These ideas led to cell theory, which states that all organisms are made of cells, all life functions occur in cells, and all cells come from other cells.
- The invention of the electron microscope in the 1950s allowed scientists to see organelles and other structures inside cells for the first time.
- There is variation in cells, but all cells have a , , , and .
-
- The plasma membrane is composed mainly of a bilayer of phospholipid molecules and forms a barrier between the cytoplasm inside the cell and the environment outside the cell. It allows only certain substances to pass in or out of the cell. Some cells have extensions of their plasma membrane with other functions, such as or .
- Cytoplasm is a thick solution that fills a cell and is enclosed by the plasma membrane. It helps give the cell shape, holds organelles, and provides a site for many of the biochemical reactions inside the cell. The liquid part of the cytoplasm is called cytosol.
- Ribosomes are small structures where proteins are made.
- Cells are usually very small, so they have a large enough surface area-to-volume ratio to maintain normal cell processes. Cells with different functions often have different shapes.
- cells do not have a . cells have a nucleus, as well as other organelles. An organelle is a structure within the cytoplasm of a cell that is enclosed within a membrane and performs a specific job.
- The is a highly organized framework of protein filaments and tubules that criss-cross the cytoplasm of a cell. It gives the cell shape and helps to hold cell structures (such as organelles) in place.
- The nucleus is the largest organelle in a eukaryotic cell. It is considered to be the cell's control center, and it contains DNA and controls gene expression, including which proteins the cell makes.
- The is an organelle that makes energy available to cells. According to the widely accepted , mitochondria evolved from prokaryotic cells that were once free-living organisms that infected or were engulfed by larger prokaryotic cells.
- The endoplasmic reticulum (ER) is an organelle that helps make and transport proteins and lipids. (RER) is studded with ribosomes. (SER) has no ribosomes.
- The is a large organelle that processes proteins and prepares them for use both inside and outside the cell. It is also involved in the transport of lipids around the cell.
- and are sac-like organelles that may be used to store and transport materials in the cell or as chambers for biochemical reactions. Lysosomes and peroxisomes are vesicles that break down foreign matter, dead cells, or poisons.
- are organelles located near the nucleus that help organize the chromosomes before cell division so each daughter cell receives the correct number of chromosomes.
- There are two basic ways that substances can cross the cell’s plasma membrane: (which requires no energy expenditure by the cell) and (which requires energy).
- No energy is needed from the cell for passive transport because it occurs when substances move naturally from an area of higher concentration to an area of lower concentration. Types of passive transport in cells include:
-
- Simple , which is the movement of a substance due to differences in concentration without any help from other molecules. This is how very small, hydrophobic molecules, such as oxygen and carbon dioxide, enter and leave the cell.
- , which is the diffusion of water molecules across the membrane.
- , which is the movement of a substance across a membrane due to differences in concentration, but only with the help of transport proteins in the membrane (such as channel proteins or carrier proteins). This is how large or hydrophilic molecules and charged ions enter and leave the cell.
- requires energy to move substances across the plasma membrane, often because the substances are moving from an area of lower concentration to an area of higher concentration or because of their large size. Two examples of active transport are the sodium-potassium pump and vesicle transport.
-
- The sodium-potassium pump moves sodium ions out of the cell and potassium ions into the cell, both against a concentration gradient, in order to maintain the proper concentrations of both ions inside and outside the cell and to thereby control membrane potential.
- Vesicle transport uses vesicles to move large molecules into or out of cells.
- Energy is the ability to do work. It is needed by every living cell to carry out life processes.
- The form of energy that living things need is chemical energy, and it comes from food. Food consists of organic molecules that store energy in their chemical bonds.
- Autotrophs (producers) make their own food. Think of plants that make food by photosynthesis. (consumers) obtain food by eating other organisms.
- Organisms mainly use the molecules and for energy. Glucose is the compact, stable form of energy that is carried in the blood and taken up by cells. ATP contains less energy and is used to power cell processes.
- The flow of energy through living things begins with , which creates glucose. The cells of organisms break down glucose and make ATP.
- is the aerobic process by which living cells break down glucose molecules, release energy, and form molecules of ATP. Overall, this three-stage process involves glucose and oxygen reacting to form carbon dioxide and water.
-
- Glycolysisno post, the first stage of cellular respiration, takes place in the cytoplasm. In this step, enzymes split a molecule of glucose into two molecules of pyruvate, which releases energy that is transferred to ATP.
- Transition Reaction takes place between glycolysis and Krebs Cycle. It is a very short reaction in which the pyruvate molecules from glycolysis are converted into Acetyl CoA in order to enter the Krebs Cycle.
- , the second stage of cellular respiration, takes place in the matrix of a mitochondrion. During this stage, two turns through the cycle result in all of the carbon atoms from the two pyruvate molecules forming carbon dioxide and the energy from their chemical bonds being stored in a total of 16 energy-carrying molecules (including four from glycolysis).
- The , he third stage of cellular respiration, takes place on the inner membrane of the mitochondrion. Electrons are transported from molecule to molecule down an electron-transport chain. Some of the energy from the electrons is used to pump hydrogen ions across the membrane, creating an electrochemical gradient that drives the synthesis of many more molecules of ATP.
- In all three stages of aerobic cellular respiration combined, as many as 38 molecules of ATP are produced from just one molecule of glucose.
- Some organisms can produce ATP from glucose by , which does not require oxygen. is an important type of anaerobic process. There are two types: alcoholic fermentation and lactic acid fermentation. Both start with glycolysis.
-
- is carried out by single-celled organisms, including yeasts and some bacteria. We use alcoholic fermentation in these organisms to make biofuels, bread, and wine.
- Lactic acid fermentationno post is undertaken by certain bacteria, including the bacteria in yogurt, and also by our muscle cells when they are worked hard and fast.
- Anaerobic respiration produces far less ATP (typically produces 2 ATP) than does aerobic cellular respiration, but it has the advantage of being much faster.
- The cell cycleno post is a repeating series of events that includes growth, DNA synthesis, and cell division.
- In a eukaryotic cell, the cell cycle has two major phases: interphase and mitotic phase. During interphase, the cell grows, performs routine life processes, and prepares to divide. During mitotic phase, first the nucleus divides (mitosis) and then the cytoplasm divides (cytokinesis), which produces two daughter cells.
-
- Until a eukaryotic cell divides, its nuclear DNA exists as a grainy material called chromatin. After DNA replicates and the cell is about to divide, the DNA condenses and coils into the X-shaped form of a chromosome. Each chromosome consists of two sister chromatids, which are joined together at a centromere.
- During mitosis, sister chromatids separate from each other and move to opposite poles of the cell. This happens in four phases: prophase, metaphase, anaphase, and telophase.
- The cell cycle is controlled mainly by regulatory proteins that signal the cell to either start or delay the next phase of the cycle at key checkpoints.
- is a disease that occurs when the cell cycle is no longer regulated, often because the cell's DNA has become damaged. Cancerous cells grow out of control and may form a mass of abnormal cells called a tumor.
In this chapter, you learned about cells and some of their functions, as well as how they pass genetic material in the form of DNA to their daughter cells. In the next chapter, you will learn how DNA is passed down to offspring, which causes traits to be inherited. These traits may be innocuous (such as eye colour) or detrimental (such as mutations that cause disease). The study of how genes are passed down to offspring is called genetics, and as you will learn in the next chapter, this is an interesting topic that is highly relevant to human health.
Chapter 4 Review
- Sequence:
- Drag and Drop:
- True or False:
- Multiple Choice:
- Briefly explain how the energy in the food you eat gets there, and how it provides energy for your neurons in the form necessary to power this process.
- Explain why the inside of the plasma membrane — the side that faces the cytoplasm of the cell — must be hydrophilic.
- Explain the relationships between interphase, mitosis, and cytokinesis.
Attributions
Figure 4.14.1
Mitochondrial Disease muscle sample by Nephron is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.
Figure 4.14.2
Aunt and Niece by Tatiana Rodriguez on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Reference
Wikipedia contributors. (2020, June 6). Mitochondrial disease. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Mitochondrial_disease&oldid=961126371
inflammation of the epididymis, which may be acute or chronic
Image shows a diagram of the cross sectional layering of heart tissues. As described in the preceding paragraph, the endocardium is a thin layer on the inside of the heart chambers, and myocardium is an extremely thick layer of cardiac muscle, and the pericardium consists of two membranes separated by fluid. The visceral pericardium envelopes the myocardium and the parietal pericardium envelopes the entire heart structure.
A biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products.
Created by CK-12 Foundation/Adapted by Christine Miller
Case Study: Flight Risk
Nineteen-year-old Malcolm is about to take his first plane flight. Shortly after he boards the plane and sits down, a man in his late sixties sits next to him in the aisle seat. About half an hour after the plane takes off, the pilot announces that she is turning the seat belt light off, and that it is safe to move around the cabin.
The man in the aisle seat — who has introduced himself to Malcolm as Willie — immediately unbuckles his seat belt and paces up and down the aisle a few times before returning to his seat. After about 45 minutes, Willie gets up again, walks some more, then sits back down and does some foot and leg exercises. After the third time Willie gets up and paces the aisles, Malcolm asks him whether he is walking so much to accumulate steps on a pedometer or fitness tracking device. Willie laughs and says no. He is actually trying to do something even more important for his health — prevent a blood clot from forming in his legs.
Willie explains that he has a chronic condition: . Although it sounds scary, his condition is currently well-managed, and he is able to lead a relatively normal lifestyle. However, it does put him at risk of developing other serious health conditions, such as deep vein thrombosis (DVT), which is when a blood clot occurs in the deep veins, usually in the legs. Air travel — and other situations where a person has to sit for a long period of time — increases the risk of DVT. Willie’s doctor said that he is healthy enough to fly, but that he should walk frequently and do leg exercises to help avoid a blood clot.
As you read this chapter, you will learn about the heart, blood vessels, and blood that make up the cardiovascular system, as well as disorders of the cardiovascular system, such as heart failure. At the end of the chapter you will learn more about why DVT occurs, why Willie has to take extra precautions when he flies, and what can be done to lower the risk of DVT and its potentially deadly consequences.
Chapter Overview: Cardiovascular System
In this chapter, you will learn about the cardiovascular system, which transports substances throughout the body. Specifically, you will learn about:
- The major components of the : the heart, blood vessels, and blood.
- The functions of the cardiovascular system, including transporting needed substances (such as oxygen and nutrients) to the cells of the body, and picking up waste products.
- How blood is oxygenated through the pulmonary circulation, which transports blood between the heart and lungs.
- How blood is circulated throughout the body through the systemic circulation.
- The components of blood — including plasma, red blood cells, white blood cells, and platelets — and their specific functions.
- Types of blood vessels — including arteries, veins, and capillaries — and their functions, similarities, and differences.
- The structure of the heart, how it pumps blood, and how contractions of the heart are controlled.
- What blood pressure is and how it is regulated.
- Blood disorders, including anemia, HIV, and leukemia.
- Cardiovascular diseases (including heart attack, stroke, and angina), and the risk factors and precursors — such as high blood pressure and atherosclerosis — that contribute to them.
As you read the chapter, think about the following questions:
- What is heart failure?Why do you think it increases the risk of DVT?
- What is a blood clot? What are possible health consequences of blood clots?
- Why do you think sitting for long periods of time increases the risk of DVT? Why does walking and exercising the legs help reduce this risk?
Attribution
Figure 14.1.1
aircraft-1583871_1920 [photo] by olivier89 from Pixabay is used under the Pixabay License (https://pixabay.com/de/service/license/).
Image shows systole and diastole of the heart. In diastole, the ventricles of the heart are relaxed and are able to receive blood from the atria. In systole, both ventricles contract, squeezing the blood out and into the pulmonary trunk and aorta.
As described in the caption.
As per caption
Image shows a diagram of the location of the sinoatrial and atrioventricular nodes. The SA node is located at the top right corner of the right atrium, and the AV node is in left wall of the right atrium, very close to the tricuspid AV valve.
Created by: CK-12/Adapted by Christine Miller
Like Pushing a Humvee Uphill
You can tell by their faces that these airmen (Figure 4.8.1) are expending a lot of trying to push this Humvee up a slope. The men are participating in a competition that tests their brute strength against that of other teams. The Humvee weighs about 13 thousand pounds (about 5,897 kilograms), so it takes every ounce of energy they can muster to move it uphill against the force of gravity. Transport of some substances across a is a little like pushing a Humvee uphill — it can't be done without adding energy.
What Is Active Transport?
Some substances can pass into or out of a cell across the without any required because they are moving from an area of higher concentration to an area of lower concentration. This type of transport is called . Other substances require energy to cross a plasma membrane, often because they are moving from an area of lower concentration to an area of higher concentration, against the concentration gradient. This type of transport is called . The energy for active transport comes from the energy-carrying molecule called (adenosine triphosphate). Active transport may also require proteins called pumps, which are embedded in the plasma membrane. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.
The Sodium-Potassium Pump
The is a mechanism of that moves sodium ions out of the cell and potassium ions into the cells — in all the trillions of in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this "uphill" process. The energy is provided by . The sodium-potassium pump also requires . Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.
To appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.
- Sodium is the principal ion in the fluid outside of cells. Normal sodium concentrations are about ten times higher outside of cells than inside of cells. To move sodium out of the cell is moving it against the concentration gradient
- Potassium is the principal ion in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells than outside of cells. To move potassium into the cell is moving it against the concentration gradient.
These differences in concentration create an electrical and chemical gradient across the , called the . Tightly controlling the membrane potential is critical for vital body functions, including the transmission of and contraction of muscles. A large percentage of the body's energy goes to maintaining this potential across the membranes of its trillions of cells with the .
Vesicle Transport
Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called . Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.
Endocytosis
is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other solid particle is engulfed, the process is called . When fluid is engulfed, the process is called .
Exocytosis
is a type of vesicle transport that moves a substance out of the cell (exo-, like "exit"). A vesicle containing the substance moves through the cytoplasm to the . Because the vesicle membrane is a like the plasma membrane, the vesicle membrane fuses with the cell membrane, and the substance is released outside the cell.
Feature: My Human Body
Maintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it's no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high blood pressure, heart disease, diabetes, and other disorders.
If you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:
- Total sodium intake should be less than 2,300 mg/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg/serving (or 5 per cent daily value).
- Total potassium intake should be 4,700 mg/day. It's easy to add potassium to the diet by choosing the right foods — and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.
Figure 4.8.5 Potassium power!
4.8 Summary
- requires to move substances across a , often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.
- The is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.
- is a type of active transport that uses to move large molecules into or out of cells.
4.8 Review Questions
- Define active transport.
- What is the sodium-potassium pump? Why is it so important?
- The drawing below shows the fluid inside and outside of a cell. The dots represent molecules of a substance needed by the cell. Explain which type of transport — active or passive — is needed to move the molecules into the cell.
- What are the similarities and differences between phagocytosis and pinocytosis?
- What is the functional significance of the shape change of the carrier protein in the sodium-potassium pump after the sodium ions bind?
- A potentially deadly poison derived from plants called ouabain blocks the sodium-potassium pump and prevents it from working. What do you think this does to the sodium and potassium balance in cells? Explain your answer.
4.8 Explore More
https://www.youtube.com/watch?v=Z_mXDvZQ6dU&feature=emb_logo
Neutrophil Phagocytosis - White Blood Cell Eats Staphylococcus Aureus Bacteria,
ImmiflexImmuneSystem, 2013.
https://www.youtube.com/watch?v=Ptmlvtei8hw
Cell Transport, The Amoeba Sisters, 2016.
Attributions
Figure 4.8.1
Humvee challenge by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 4.8.2
Sodium Potassium Pump by Christine Miller is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 4.8.3
Cytosis by Manu5 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 4.8.4
Endocytosis and Exocytosis by Christine Miller is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 4.8.5
- Canteloupes. Image Number K7355-11 by Scott Bauer/ USDA on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
- Spinach by chiara conti on Unsplash is used under the Unsplash license (https://unsplash.com/license).
- Eleven long purple eggplants by JVRKPRASAD on Wikimedia commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
- Bananas by Marco Antonio Victorino on Pexels is used under the Pexels license (https://www.pexels.com/license/).
- Potato picking by Nic D on Unsplash is used under the Unsplash license (https://unsplash.com/license).
- Maldives by Sebastian Pena Lambarri on Unsplash is used under the Unsplash license (https://unsplash.com/license).
Figure 4.8.6
Active Transport by Christine Miller is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Amoeba Sisters. (2016, June 24). Cell transport [digital image]. YouTube. https://www.youtube.com/watch?v=Ptmlvtei8hw&feature=youtu.be
ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis - White blood cell eats staphylococcus aureus bacteria. YouTube. https://www.youtube.com/watch?v=Z_mXDvZQ6dU
Mayo Clinic Staff. (n.d.). Diabetes [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/diabetes/symptoms-causes/syc-20371444
Mayo Clinic Staff. (n.d.). High blood pressure (hypertension) [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/symptoms-causes/syc-20373410
Mayo Clinic Staff. (n.d.). Heart disease [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/heart-disease/symptoms-causes/syc-20353118
Wikipedia contributors. (2020, June 19). Ouabain. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Ouabain&oldid=963440756
A rigid organ that constitutes part of the vertebrate skeleton in animals.
As per caption.
Image shows before and after xrays and photos of a patient who has been using a brace to treat their condition. The change in spinal curvature improved from 56 degrees to 27 degrees; possibly preventing the need for surgery.
Figure 7.4.1 Construction — It's important to have the right materials for the job.
The Right Material for the Job
Building a house is a big job and one that requires a lot of different materials for specific purposes. As you can see in Figure 7.4.1, many different types of materials are used to build a complete house, but each type of material fulfills certain functions. You wouldn't use insulation to cover your roof, and you wouldn't use lumber to wire your home. Just as a builder chooses the appropriate materials to build each aspect of a home (wires for electrical, lumber for framing, shingles for roofing), your body uses the right cells for each type of role. When many cells work together to perform a specific function, this is termed a .
Tissues
Groups of connected cells form tissues. The cells in a tissue may all be the same type, or they may be of multiple types. In either case, the cells in the tissue work together to carry out a specific function, and they are always specialized to be able to carry out that function better than any other type of tissue. There are four main types of human tissues: connective, epithelial, muscle, and nervous tissues. We use tissues to build organs and organ systems. The 200 types of cells that the body can produce based on our single set of DNA can create all the types of tissue in the body.
Epithelial Tissue
is made up of cells that line inner and outer body surfaces, such as the skin and the inner surface of the digestive tract. Epithelial tissue that lines inner body surfaces and body openings is called mucous membrane. This type of epithelial tissue produces mucus, a slimy substance that coats mucous membranes and traps pathogens, particles, and debris. Epithelial tissue protects the body and its internal organs, secretes substances (such as hormones) in addition to mucus, and absorbs substances (such as nutrients).
The key identifying feature of epithelial tissue is that it contains a free surface and a basement membrane. The free surface is not attached to any other cells and is either open to the outside of the body, or is open to the inside of a hollow organ or body tube. The basement membrane anchors the epithelial tissue to underlying cells.
Epithelial tissue is identified and named by shape and layering. Epithelial cells exist in three main shapes: squamous, cuboidal, and columnar. These specifically shaped cells can, depending on function, be layered several different ways: simple, stratified, pseudostratified, and transitional.
Epithelial tissue forms coverings and linings and is responsible for a range of functions including diffusion, absorption, secretion and protection. The shape of an epithelial cell can maximize its ability to perform a certain function. The thinner an epithelial cell is, the easier it is for substances to move through it to carry out diffusion and/or absorption. The larger an epithelial cell is, the more room it has in its cytoplasm to be able to make products for secretion, and the more protection it can provide for underlying tissues. Their are three main shapes of epithelial cells: squamous (which is shaped like a pancake- flat and oval), cuboidal (cube shaped), and columnar (tall and rectangular).
Figure 7.4.2 The shape of epithelial tissues is important.
Epithelial tissue will also organize into different layerings depending on their function. For example, multiple layers of cells provide excellent protection, but would no longer be efficient for diffusion, whereas a single layer would work very well for diffusion, but no longer be as protective; a special type of layering called transitional is needed for organs that stretch, like your bladder. Your tissues exhibit the layering that makes them most efficient for the function they are supposed to perform. There are four main layerings found in epithelial tissue: simple (one layer of cells), stratified (many layers of cells), pseudostratified (appears stratified, but upon closer inspection is actually simple), and transitional (can stretch, going from many layers to fewer layers).
Figure 7.4.3 The layerings found in epithelial tissues is important.
See Table 7.4.1 for a summary of the different layering types and shapes epithelial cells can form and their related functions and locations.
Table 7.4.1
Summary of Epithelial Tissue Cells
So far, we have identified epithelial tissue based on shape and layering. The representative diagrams we have seen so far are helpful for visualizing the tissue structures, but it is important to look at real examples of these cells. Since cells are too tiny to see with the naked eye, we rely on microscopes to help us study them. is the study of the microscopic anatomy and cells and tissues. See Table 7.4.2 to see some examples of slides of epithelial tissues prepared for the purpose of histology.
Table 7.4.2
Epithelial Tissues and Histological Samples
Epithelial Tissue Type | Tissue Diagram | Histological Sample |
Stratified squamous
(from skin) |
||
Simple cuboidal
(from kidney tubules) |
||
Pseudostratified ciliated columnar
(from trachea) |
Connective Tissue
Bone and blood are examples of connective tissue. is very diverse. In general, it forms a framework and support structure for body tissues and organs. It's made up of living cells separated by non-living material, called , which can be solid or liquid. The extracellular matrix of bone, for example, is a rigid mineral framework. The extracellular matrix of blood is liquid plasma.
The key identifying feature of connective tissue is that is is composed of a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, based on the nature of the matrix. They look very different from one another, which is a reflection of their different functions:
- Fibrous connective tissue: is characterized by a matrix which is flexible and is made of protein fibres including collagen, elastin and possibly reticular fibres. These tissues are found making up tendons, ligaments, and body membranes.
- Supportive connective tissue: is characterized by a solid matrix and is what is used to make bone and cartilage. These tissues are used for support and protection.
- Fluid connective tissue: is characterized by a fluid matrix and includes both blood and lymph.
Fibrous Connective Tissue
Fibrous connective tissue contains cells called . These cells produce fibres of collagen, elastin, or reticular fibre which makes up the matrix of this type of connective tissue. Based on how tightly packed these fibres are and how they are oriented changes the properties, and therefore the function of the fibrous connective tissue.
- Loose fibrous connective tissue: composed of a loose and disorganized weave of collagen and elastin fibres, creating a tissue that is thin and flexible, yet still tough. This tissue, which is also sometimes referred to as "areolar tissue", is found in membranes and surrounding blood vessels and most body organs. As you can see from the diagram in Figure 7.4.4, loose fibrous connective tissue fulfills the definition of connectives tissue since it is a scattering of cells (fibroblasts) in a non-cellular matrix (a mesh of collagen and elastin fibres). There are two types of specialized loose fibrous connective tissue: reticular and adipose. Adipose tissue stores fat and reticular tissue forms the spleen and lymph nodes.
- Dense Fibrous Connective Tissue: composed of a dense mat of parallel collagen fibres and a scattering of fibroblasts, creating a tissue that is very strong. Dense fibrous connective tissue forms tendons and ligaments, which connect bones to muscles and/or bones to neighbouring bones.
Supportive Connective Tissue
Supportive connective tissue exhibits the defining feature of connective tissue in that it is a scattering of cells in a non-cellular matrix; what sets it apart from other connective tissues is its solid matrix. In this tissue group, the matrix is solid- either bone or cartilage. While fibrous connective tissue contained cells called fibroblasts which produced fibres, supportive connective tissue contains cells that either create bone () or cells that create cartilage ().
Cartilage
Chondrocytes produce the cartilage matrix in which they reside. Cartilage is made up of protein fibres and chondrocytes in lacunae. This is tissue is strong yet flexible and is used many places in the body for protection and support. Cartilage is one of the few tissues that is not vascular (doesn't have a direct blood supply) meaning it relies on diffusion to obtain nutrients and gases; this is the cause of slow healing rates in injuries involving cartilage. There are three main types of cartilage:
- Hyaline cartilage: a smooth, strong and flexible tissue. Found at the ends of ribs and long bones, in the nose, and comprising the entire fetal skeleton.
- Fibrocartilage: a very strong tissue containing thick bundles of collagen. Found in joints that need cushioning from high impact (knees, jaw).
- Elastic cartilage: contains elastic fibres in addition to collagen, giving support with the benefit of elasticity. Found in earlobes and the epiglottis.
Bone
Osteocytes produce the bone matrix in which they reside. Since bone is very solid, these cells reside in small spaces called . This bone tissue is composed of collagen fibres embedded in calcium phosphate giving it strength without brittleness. There are two types of bone: compact and spongy.
- Compact bone: has a dense matrix organized into cylindrical units called osteons. Each osteon contains a central canal (sometimes called a Harversian Canal) which allows for space for blood vessels and nerves, as well as concentric rings of bone matrix and osteocytes in lacunae, as per the diagram here. Compact bone is found in long bones and forms a shell around spongy bone.
- Spongy bone: a very porous type of bone which most often contains bone marrow. It is found at the end of long bones, and makes up the majority of the ribs, shoulder blades and flat bones of the cranium.
Fluid Connective Tissue
Fluid connective tissue has a matrix that is fluid; unlike the other two categories of connective tissue, the cells that reside in the matrix do not actually produce the matrix. Fibroblasts make the fibrous matrix, chondrocytes make the cartilaginous matrix, osteocytes make the bony matrix, yet blood cells do not make the fluid matrix of either lymph or plasma. This tissue still fits the definition of connective tissue in that it is still a scattering of cells in a non-cellular matrix.
There are two types of fluid connective tissue:
- Blood: blood contains three types of cells suspended in plasma, and is contained in the cardiovascular system.
- Eryththrocytes, more commonly called red blood cells, are present in high numbers (roughly 5 million cells per mL) and are responsible for delivering oxygen from to the lungs to all the other areas of the body. These cells are relatively small in size with a diameter of around 7 micrometres and live no longer than 120 days.
- Leukocytes, often referred to as white blood cells, are present in lower numbers (approximately 5 thousand cells per mL) are responsible for various immune functions. They are typically larger than erythrocytes, but can live much longer, particularly white blood cells responsible for long term immunity. The number of leukocytes in your blood can go up or down based on whether or not you are fighting an infection.
- Thrombocytes, also known as platelets, are very small cells responsible for blood clotting. Thrombocytes are not actually true cells, they are fragments of a much larger cell called a megakaryocyte.
- Lymph: contains a liquid matrix and white blood cells and is contained in the lymphatic system, which ultimately drains into the cardiovascular system.
Figure 7.4.11 A stained lymphocyte surrounded by red blood cells viewed using a light microscope.
Muscular Tissue
is made up of cells that have the unique ability to contract- which is the defining feature of muscular tissue. There are three major types of muscle tissue, as pictured in Figure 7.4.12 skeletal, smooth, and cardiac muscle tissues.
Skeletal Muscle
Skeletal muscles are voluntary muscles, meaning that you exercise conscious control over them. Skeletal muscles are attached to bones by tendons, a type of connective tissue. When these muscles shorten to pull on the bones to which they are attached, they enable the body to move. When you are exercising, reading a book, or making dinner, you are using skeletal muscles to move your body to carry out these tasks.
Under the microscope, skeletal muscles are striated (or striped) in appearance, because of their internal structure which contains alternating protein fibres of actin and myosin. Skeletal muscle is described as multinucleated, meaning one "cell" has many nuclei. This is because in utero, individual cells destined to become skeletal muscle fused, forming muscle fibres in a process known as myogenesis. You will learn more about skeletal muscle and how it contracts in the Muscular System.
Smooth Muscle
Smooth muscles are nonstriated muscles- they still contain the muscle fibres actin and myosin, but not in the same alternating arrangement seen in skeletal muscle. Smooth muscle is found in the tubes of the body - in the walls of blood vessels and in the reproductive, gastrointestinal, and respiratory tracts. Smooth muscles are not under voluntary control meaning that they operate unconsciously, via the autonomic nervous system. Smooth muscles move substances through a wave of contraction which cascades down the length of a tube, a process termed .
Watch the YouTube video "What is Peristalsis" by Mister Science to see peristalsis in action.
https://www.youtube.com/watch?v=kVjeNZA5pi4
What is Peristalsis, Mister Science, 2018.
Cardiac Muscle
Cardiac muscles work involuntarily, meaning they are regulated by the autonomic nervous system. This is probably a good thing, since you wouldn't want to have to consciously concentrate on keeping your heart beating all the time! Cardiac muscle, which is found only in the heart, is mononucleated and striated (due to alternating bands of myosin and actin). Their contractions cause the heart to pump blood. In order to make sure entire sections of the heart contract in unison, cardiac muscle tissue contains special cell junctions called , which conduct the electrical signals used to "tell" the chambers of the heart when to contract.
Nervous Tissue
is made up of neurons and a group of cells called neuroglia (also known as glial cells). Nervous tissue makes up the central nervous system (mainly the brain and spinal cord) and peripheral nervous system (the network of nerves that runs throughout the rest of the body). The defining feature of nervous tissue is that it is specialized to be able to generate and conduct nerve impulses. This function is carried out by neurons, and the purpose of neuroglia is to support neurons.
A neuron has several parts to its structure:
- Dendrites which collect incoming nerve impulses
- A cell body, or soma, which contains the majority of the neuron's organelles, including the nucleus
- An axon, which carries nerve impulses away from the soma, to the next neuron in the chain
- A myelin sheath, which encases the axon and increases that rate at which nerve impulses can be conducted
- Axon terminals, which maintain physical contact with the dendrites of neighbouring neurons
Neuroglia can be understood as support staff for the neuron. The neurons have such an important job, they need cells to bring them nutrients, take away cell waste, and build their mylein sheath. There are many types of neuroglia, which are categorized based on their function and/or their location in the nervous system. Neuroglia outnumber neurons by as much as 50 to 1, and are much smaller. See the diagram in 7.4.17 to compare the size and number of neurons and neuroglia.
Try out this memory game to test your tissues knowledge:
7.4 Summary
- Tissues are made up of cells working together.
- There are four main types of tissues: epithelial, connective, muscular and nervous.
- Epithelial tissue makes up the linings and coverings of the body and is characterized by having a free surface and a basement membrane. Types of epithelial tissue are distinguished by shape of cell (squamous, cuboidal or columnar) and layering (simple, stratified, pseudostratified and transitional). Different epithelial tissues can carry out diffusion, secretion, absorption, and/or protection depending on their particular cell shape and layering.
- Connective tissue provides structure and support for the body and is characterized as a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, each characterized by a particular type of matrix:
- Fibrous connective tissue contains protein fibres. Both loose and dense fibrous connective tissue belong in this category.
- Supportive connective tissue contains a very solid matrix, and includes both bone and cartilage.
- Fluid connective tissue contains cells in a fluid matrix with the two types of blood and lymph.
- Muscular tissue's defining feature is that it is contractile. There are three types of muscular tissue: skeletal muscle which is found attached to the skeleton for voluntary movement, smooth muscle which moves substances through body tubes, and cardiac muscle which moves blood through the heart.
- Nervous tissue contains specialized cells called neurons which can conduct electrical impulses. Also found in nervous tissue are neuroglia, which support neurons by providing nutrients, removing wastes, and creating myelin sheath.
7.4 Review Questions
- Define the term tissue.
- If a part of the body needed a lining that was both protective, but still able to absorb nutrients, what would be the best type of epithelial tissue to use?
- Where do you find skeletal muscle? Smooth muscle? Cardiac muscle?
- What are some of the functions of neuroglia?
7.4 Explore More
https://www.youtube.com/watch?v=O0ZvbPak4ck
Types of Human Body Tissue, MoomooMath and Science, 2017.
https://www.youtube.com/watch?v=uHbn7wLN_3k
How to 3D print human tissue - Taneka Jones, TED-Ed, 2019.
https://www.youtube.com/watch?v=1Qfmkd6C8u8
How bones make blood - Melody Smith, TED-Ed, 2020.
Attributions
Figure 7.4.1
- Construction man kneeling in front of wall by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Beige wooden frame by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Tambour on green by Pierre Châtel-Innocention Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Tags: Construction Studs Plumbing Wiring by JWahl on Pixabay is used under the Pixabay License (https://pixabay.com/es/service/license/).
Figure 7.4.2 and Figure 7.4.3
- Simple columnar epithelium tissue by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
- Simple cuboidal epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
- Simple squamous epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.4
Loose fibrous connective tissue by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.
Figure 7.4.5
Connective Tissue: Loose Aerolar by Berkshire Community College Bioscience Image Library on Flickr is used under a CC0 1.0 Universal public domain dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
Figure 7.4.6
Dense Fibrous Connective Tissue by by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.
Figure 7.4.7
Dense_connective_tissue-400x by J Jana on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.8
Types_of_Cartilage-new by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 7.4.9
Compact_bone_histology_2014 by Athikhun.suw on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.10
Bone_normal_and_degraded_micro_structure by Gtirouflet on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.11
Lymphocyte2 by NicolasGrandjean on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. [No machine-readable author provided. NicolasGrandjean is assumed, based on copyright claims.]
Figure 7.4.12
Skeletal_muscle_横纹肌1 by 乌拉跨氪 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.13
Smooth_Muscle_new by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 7.4.14
Peristalsis by OpenStax on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 7.4.15
400x Cardiac Muscle by Jessy731 on Flickr is used and adapted by Christine Miller under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 7.4.16
Neuron.svg by User:Dhp1080 on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.17
400x Nervous Tissue by Jessy731 on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Table 7.4.1
Summary of Epithelial Tissue Cells, by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Table 7.4.2
- Epithelial_Tissues_Stratified_Squamous_Epithelium_(40230842160) by
Berkshire Community College Bioscience Image Library on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license. - Simple cuboidal epithelial tissue histology by Berkshire Community College on Flickr is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
- Pseudostratified_Epithelium by OpenStax College 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, April 25). Figure 4.8 Summary of epithelial tissue cells [digital image]. In Anatomy and Physiology (Section 4.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-2-epithelial-tissue
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, April 25). Figure 4.16 Types of cartilage [digital image]. In Anatomy and Physiology (Section 4.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-3-connective-tissue-supports-and-protects
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, April 25). Figure 10.23 Smooth muscle [digital micrograph]. In Anatomy and Physiology (Section 10.8). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-8-smooth-muscle (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
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, April 25). Figure 22.5 Pseudostratified ciliated columnar epithelium [digital micrograph]. In Anatomy and Physiology (Section 22.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-1-organs-and-structures-of-the-respiratory-system
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, April 25). Figure 23.5 Peristalsis [diagram]. In Anatomy and Physiology (Section 23.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/23-2-digestive-system-processes-and-regulation
Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/watch?v=kVjeNZA5pi4
MoomooMath and Science. (2017, May 18). Types of human body tissue. YouTube. https://www.youtube.com/watch?v=O0ZvbPak4ck&feature=youtu.be
Open Stax. (2016, May 27). Figure 6 Loose connective tissue [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues
Open Stax. (2016, May 27). Figure 7 Fibrous connective tissue from the tendon [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues
TED-Ed. (2019, October 17). How to 3D print human tissue - Taneka Jones. YouTube. https://www.youtube.com/watch?v=uHbn7wLN_3k&feature=youtu.be
TED-Ed. (2020, January 27). How bones make blood - Melody Smith. YouTube. https://www.youtube.com/watch?v=1Qfmkd6C8u8&feature=youtu.be
A sequence of nucleotides in DNA or RNA that codes for a molecule that has a function.
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 , 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 and not , 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 — 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
Created by CK-12 Foundation/Adapted by Christine Miller
Kidneys on the Menu
Pictured in Figure 16.4.1 is a steak and kidney pie; this savory dish is a British favorite. When kidneys are on a menu, they typically come from sheep, pigs, or cows. In these animals (as in the human animal), kidneys are the main organs of excretion.
Location of the Kidneys
The two bean-shaped are located high in the back of the , one on each side of the spine. Both kidneys sit just below the , the large breathing muscle that separates the abdominal and thoracic cavities. As you can see in the following figure, the right kidney is slightly smaller and lower than the left kidney. The right kidney is behind the , and the left kidney is behind the . The location of the liver explains why the right kidney is smaller and lower than the left.
Kidney Anatomy
The shape of each kidney gives it a convex side (curving outward) and a concave side (curving inward). You can see this clearly in the detailed diagram of kidney anatomy shown in Figure 16.4.3. The concave side is where the renal artery enters the kidney, as well as where the renal vein and ureter leave the kidney. This area of the kidney is called the . The entire kidney is surrounded by tough fibrous tissue — called the — which, in turn, is surrounded by two layers of protective, cushioning fat.
Internally, each kidney is divided into two major layers: the outer and the inner (see Figure 16.4.3 above). These layers take the shape of many cone-shaped renal lobules, each containing renal cortex surrounding a portion of medulla called a . Within the renal pyramids are the structural and functional units of the kidneys, the tiny . Between the renal pyramids are projections of cortex called . The tip, or papilla, of each pyramid empties urine into a minor calyx (chamber). Several minor calyces empty into a major calyx, and the latter empty into the funnel-shaped cavity called the , which becomes the ureter as it leaves the kidney.
Renal Circulation
The renal circulation is an important part of the kidney’s primary function of filtering waste products from the blood. is supplied to the kidneys via the renal arteries. The right renal artery supplies the right kidney, and the left renal artery supplies the left kidney. These two arteries branch directly from the aorta, which is the largest artery in the body. Each kidney is only about 11 cm (4.4 in) long, and has a mass of just 150 grams (5.3 oz), yet it receives about ten per cent of the total output of blood from the heart. Blood is filtered through the kidneys every 3 minutes, 24 hours a day, every day of your life.
As indicated in Figure 16.4.4, each renal artery carries blood with waste products into the kidney. Within the kidney, the renal artery branches into increasingly smaller that extend through the between the . These arteries, in turn, branch into arterioles that penetrate the renal pyramids. Blood in the arterioles passes through , the structures that actually filter the blood. After blood passes through the nephrons and is filtered, the clean blood moves through a network of venules that converge into small . Small veins merge into increasingly larger ones, and ultimately into the renal vein, which carries clean blood away from the kidney to the inferior .
Nephron Structure and Function
Figure 16.4.4 gives an indication of the complex structure of a nephron. The is the basic structural and functional unit of the kidney, and each kidney typically contains at least a million of them. As blood flows through a nephron, many materials are filtered out of the blood, needed materials are returned to the blood, and the remaining materials form urine. Most of the waste products removed from the blood and excreted in urine are byproducts of . At least half of the waste is , a waste product produced by . Another important waste is , produced in catabolism.
Components of a Nephron
Figure 16.4.5 shows in greater detail the components of a . Each nephron is composed of an initial filtering component that consists of a network of capillaries called the (plural, glomeruli), which is surrounded by a space within a structure called (also known as the Bowman's capsule). Extending from glomerular capsule is the . The proximal end (nearest glomerular capsule) of the renal tubule is called the . From here, the renal tubule continues as a loop (known as the ) (also known as the loop of the nephron), which in turn becomes the . The latter finally joins with a collecting duct. As you can see in the diagram, arterioles surround the total length of the renal tubule in a mesh called the .
Function of a Nephron
The simplified diagram of a nephron in Figure 16.4.6 shows an overview of how the nephron functions. Blood enters the nephron through an arteriole called the afferent arteriole. Next, some of the blood passes through the capillaries of the glomerulus. Any blood that doesn’t pass through the glomerulus — as well as blood after it passes through the glomerular capillaries — continues on through an arteriole called the efferent arteriole. The efferent arteriole follows the renal tubule of the nephron, where it continues playing a role in nephron functioning.
Filtration
As blood from the afferent arteriole flows through the glomerular capillaries, it is under pressure. Because of the pressure, water and solutes are filtered out of the blood and into the space made by glomerular capsule, almost like the water you cook pasta is is filtered out through a strainer. This is the filtration stage of nephron function. The filtered substances — called — pass into glomerular capsule, and from there into the proximal end of the . Anything too large to move through the pores in the glomerulus, such as blood cells, large proteins, etc., stay in the cardiovascular system. At this stage, filtrate (fluid in the nephron) includes water, salts, organic solids (such as nutrients), and waste products of metabolism (such as urea).
Reabsorption and Secretion
As filtrate moves through the renal tubule, some of the substances it contains are reabsorbed from the filtrate back into the blood in the efferent arteriole (via ). This is the reabsorption stage of nephron function and it is about returning "the good stuff" back to the blood so that it doesn't exit the body in urine. About two-thirds of the filtered salts and water, and all of the filtered organic solutes (mainly and ) are reabsorbed from the filtrate by the blood in the peritubular capillary network. occurs mainly in the proximal convoluted tubule and the loop of Henle, as seen in Figure 16.4.7.
At the distal end of the renal tubule, some additional reabsorption generally occurs. This is also the region of the tubule where other substances from the blood are added to the filtrate in the tubule. The addition of other substances to the filtrate from the blood is called . Both reabsorption and secretion (shown in Figure 16.4.7) in the distal convoluted tubule are largely under the control of endocrine hormones that maintain of water and mineral salts in the blood. These hormones work by controlling what is reabsorbed into the blood from the filtrate and what is secreted from the blood into the filtrate to become urine. For example, causes more calcium to be reabsorbed into the blood and more phosphorus to be secreted into the filtrate.
Collection of Urine and Excretion
By the time the filtrate has passed through the entire renal tubule, it has become the liquid waste known as . Urine empties from the distal end of the into a . From there, the urine flows into increasingly larger collecting ducts. As urine flows through the system of collecting ducts, more water may be reabsorbed from it. This will occur in the presence of from the posterior . This hormone makes the collecting ducts permeable to water, allowing water molecules to pass through them into capillaries by , while preventing the passage of ions or other solutes. As much as 75% of the water may be reabsorbed from urine in the collecting ducts, making the urine more concentrated.
Urine finally exits the largest collecting ducts through the renal papillae. It empties into the renal calyces, and finally into the . From there, it travels through the to the for eventual excretion from the body. An average of roughly 1.5 litres (a little over 6 cups) of urine is excreted each day. Normally, urine is yellow or amber in colour (see Figure 16.4.8). The darker the colour, generally speaking, the more concentrated the urine is.
Besides filtering blood and forming urine for excretion of soluble wastes, the kidneys have several vital functions in maintaining body-wide . Most of these functions are related to the composition or volume of urine formed by the kidneys. The kidneys must maintain the proper balance of water and salts in the body, normal , and the correct range of blood . Through the processes of absorption and secretion by nephrons, more or less water, salt ions, acids, or bases are returned to the blood or excreted in urine, as needed, to maintain homeostasis.
Blood Pressure Regulation
The kidneys do not control homeostasis all alone. As indicated above, endocrine hormones are also involved. Consider the regulation of blood pressure by the kidneys. Blood pressure is the pressure exerted by blood on the walls of the arteries. The regulation of blood pressure is part of a complex system, called the renin-angiotensin-aldosterone system. This system regulates the concentration of sodium in the blood to control blood pressure.
The renin-angiotensin-aldosterone system is put into play when the concentration of sodium ions in the blood falls lower than normal. This causes the kidneys to secrete an enzyme called into the blood. It also causes the liver to secrete a protein called angiotensinogen. Renin changes angiotensinogen into a proto-hormone called angiotensin I. This is converted to angiotensin II by an enzyme (angiotensin-converting enzyme) in lung capillaries.
Angiotensin II is a potent hormone that causes arterioles to constrict. This, in turn, increases blood pressure. Angiotensin II also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the kidneys to increase the reabsorption of sodium ions and water from the filtrate into the blood. This returns the concentration of sodium ions in the blood to normal. The increased water in the blood also increases blood volume and blood pressure.
Other Kidney Hormones
Hormones other than renin are also produced and secreted by the kidneys. These include calcitriol and erythropoietin.
- is secreted by the kidneys in response to low levels of calcium in the blood. This hormone stimulates uptake of calcium by the intestine, thus raising blood levels of calcium.
- is secreted by the kidneys in response to low levels of oxygen in the blood. This hormone stimulates erythropoiesis, which is the production of in bone marrow. Extra red blood cells increase the level of oxygen carried in the blood.
Feature: Human Biology in the News
Kidney failure is a complication of common disorders including and . It is estimated that approximately 12.5% of Canadians have some form of kidney disease. If the disease is serious, the patient must either receive a donated kidney or have frequent hemodialysis, a medical procedure in which the blood is artificially filtered through a machine. Transplant generally results in better outcomes than hemodialysis, but demand for organs far outstrips the supply. The average time on the organ donation waitlist for a kidney is four years. There are over 3,000 Canadians on the wait list for a kidney transplant and some will die waiting for a kidney to become available.
For the past decade, Dr. William Fissell, a kidney specialist at Vanderbilt University, has been working to create an implantable part-biological and part-artificial kidney. Using microchips like those used in computers, he has produced an artificial kidney small enough to implant in the patient’s body in place of the failed kidney. According to Dr. Fissell, the artificial kidney is “... a bio-hybrid device that can mimic a kidney to remove enough waste products, salt, and water to keep a patient off [hemo]dialysis.”
The filtration system in the artificial kidney consists of a stack of 15 microchips. Tiny pores in the microchips act as a scaffold for the growth of living kidney cells that can mimic the natural functions of the kidney. The living cells form a membrane to filter the patient’s blood as a biological kidney would, but with less risk of rejection by the patient’s immune system, because they are embedded within the device. The new kidney doesn’t need a power source, because it uses the natural pressure of blood flowing through arteries to push the blood through the filtration system. A major part of the design of the artificial organ was devoted to fine tuning the fluid dynamics so blood flows through the device without clotting.
Because of the potential life-saving benefits of the device, the implantable kidney was given fast-track approval for testing in people by the U.S. Food and Drug Administration. The artificial kidney is expected to be tested in pilot trials by 2018. Dr. Fissell says he has a long list of patients eager to volunteer for the trials.
16.4 Summary
- The two bean-shaped kidneys are located high in the back of the abdominal cavity on either side of the spine. A renal artery connects each kidney with the aorta, and transports unfiltered blood to the kidney. A renal vein connects each kidney with the inferior vena cava and transports filtered blood back to the circulation.
- The kidney has two main layers involved in the filtration of blood and formation of urine: the outer cortex and inner medulla. At least a million nephrons — which are the tiny functional units of the kidney — span the cortex and medulla. The entire kidney is surrounded by a fibrous capsule and protective fat layers.
- As blood flows through a nephron, many materials are filtered out of the blood, needed materials are returned to the blood, and the remaining materials are used to form urine.
- In each nephron, the glomerulus and surrounding Bowman’s capsule form the unit that filters blood. From Bowman’s capsule, the material filtered from blood (called filtrate) passes through the long renal tubule. As it does, some substances are reabsorbed into the blood, and other substances are secreted from the blood into the filtrate, finally forming urine. The urine empties into collecting ducts, where more water may be reabsorbed.
- The kidneys control homeostasis with the help of endocrine hormones. The kidneys, for example, are part of the renin-angiotensin-aldosterone system that regulates the concentration of sodium in the blood to control blood pressure. In this system, the enzyme renin secreted by the kidneys works with hormones from the liver and adrenal gland to stimulate nephrons to reabsorb more sodium and water from urine.
- The kidneys also secrete endocrine hormones, including calcitriol — which helps control the level of calcium in the blood — and erythropoietin, which stimulates bone marrow to produce red blood cells.
16.4 Review Questions
- Contrast the renal artery and renal vein.
- Identify the functions of a nephron. Describe in detail what happens to fluids (blood, filtrate, and urine) as they pass through the parts of a nephron.
- Identify two endocrine hormones secreted by the kidneys, along with the functions they control.
- Name two regions in the kidney where water is reabsorbed.
- Is the blood in the glomerular capillaries more or less filtered than the blood in the peritubular capillaries? Explain your answer.
- What do you think would happen if blood flow to the kidneys is blocked?
16.4 Explore More
https://youtu.be/FN3MFhYPWWo
How do your kidneys work? - Emma Bryce, TED-Ed, 2015.
https://youtu.be/es-t8lO1KpA
Urine Formation, Hamada Abass, 2013.
https://youtu.be/bX3C201O4MA
Printing a human kidney - Anthony Atala, TED-Ed, 2013.
Attributions
Figure 16.4.1
Steak and Kidney Pie by Charles Haynes on Flickr is used under a CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0/) license.
Figure 16.4.2
Gray Kidneys by Henry Vandyke Carter (1831-1897) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain). (Bartleby.com: Gray’s Anatomy, Plate 1120).
Figure 16.4.3
Blausen_0592_KidneyAnatomy_01 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.4
Diagram_showing_how_the_kidneys_work_CRUK_138.svg by Cancer Research UK on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 16.4.5
Blood_Flow_in_the_Nephron by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.6
1024px-Physiology_of_Nephron by Madhero88 on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.7
Nephron_Secretion_Reabsorption by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.8
Urine by User:Markhamilton at English Wikipedia on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 16.4.9
Renin_Angiotensin_System-01 by OpenStax College 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 25.10 Blood flow in the nephron [digital image]. In Anatomy and Physiology (Section 25.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/25-3-gross-anatomy-of-the-kidney
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 25.17 Locations of secretion and reabsorption in the nephron [digital image]. In Anatomy and Physiology (Section 25.6). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/25-6-tubular-reabsorption
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 26.14 The renin-angiotensin system [digital image]. In Anatomy and Physiology (Section 26.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/26-3-electrolyte-balance
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436
Hamada Abass. (2013). Urine formation. YouTube. https://www.youtube.com/watch?v=es-t8lO1KpA&feature=youtu.be
TED-Ed. (2015, February 9). How do your kidneys work? - Emma Bryce. YouTube. https://www.youtube.com/watch?v=FN3MFhYPWWo&feature=youtu.be
TED-Ed. (2013, March 15). Printing a human kidney - Anthony Atala. YouTube. https://www.youtube.com/watch?v=bX3C201O4MA&feature=youtu.be
A substance that takes part in and undergoes change during a chemical reaction.