12.5 Physical Exercise
Stroller Moms
These moms (Figure 12.5.1) are setting a great example for their children by engaging in physical exercise. Adopting a habit of regular physical exercise is one of the most important ways to maintain fitness and good health. From higher self-esteem to a healthier heart, physical exercise can have a positive effect on virtually all aspects of health, including physical, mental, and emotional health.
What Is Physical Exercise?
is any bodily activity that enhances or maintains physical fitness and overall health and wellness. We generally think of physical exercise as activities that are undertaken for the main purpose of improving physical fitness and health. However, physical activities that are undertaken for other purposes may also count as physical exercise. Scrubbing a floor, raking a lawn, or playing active games with young children or a pet are all activities that can have fitness and health benefits, even though they generally are not done mainly for this purpose.
How much physical exercise should people get? In the Canada, both the Canadian Food Guide and the Canadian Society for Exercise Physiology recommend that every child and adult who is able should participate in moderate exercise for a minimum of 60 minutes a day. This might include walking, swimming, and/or household or yard work.
Types of Physical Exercise
Physical exercise can be classified into three types, depending on the effects it has on the body: aerobic exercise, anaerobic exercise, and flexibility exercise. Many specific examples of physical exercise (including playing soccer and rock climbing) can be classified as more than one type.
Aerobic Exercise
is any physical activity in which muscles are used at well below their maximum contraction strength, but for long periods of time. Aerobic exercise uses a relatively high percentage of slow-twitch muscle fibres that consume a large amount of oxygen. The main goal of aerobic exercise is to increase cardiovascular endurance, although it can have many other benefits, including muscle toning. Examples of aerobic exercise include cycling, swimming, brisk walking, jumping rope, rowing, hiking, tennis, and kayaking as shown in Figure 12.5.2 .
Anaerobic Exercise
is any physical activity in which muscles are used at close to their maximum contraction strength, but for relatively short periods of time. Anaerobic exercise uses a relatively high percentage of fast-twitch muscle fibres that consume a small amount of oxygen. Goals of anaerobic exercise include building and strengthening muscles, as well as improving bone strength, balance, and coordination. Examples of anaerobic exercise include push-ups, lunges, sprinting, interval training, resistance training, and weight training (such as biceps curls with a dumbbell, as pictured in Figure 12.5.3).
Flexibility Exercise
is any physical activity that stretches and lengthens muscles. Goals of flexibility exercise include increasing joint flexibility, keeping muscles limber, and improving the range of motion, all of which can reduce the risk of injury. Examples of flexibility exercise include stretching, yoga (as in Figure 12.5.4), and tai chi.
Health Benefits of Physical Exercise
Many studies have shown that physical exercise is positively correlated with a diversity of health benefits. Some of these benefits include maintaining physical fitness, losing weight and maintaining a healthy weight, regulating digestive health, building and maintaining healthy bone density, increasing muscle strength, improving joint mobility, strengthening the immune system, boosting cognitive ability, and promoting psychological well-being. Some studies have also found a significant positive correlation between exercise and both quality of life and life expectancy. People who participate in moderate to high levels of physical activity have been shown to have lower mortality rates than people of the same ages who are not physically active and daily exercise has been shown to increase life expectancy up to an average of five years.
The underlying physiological mechanisms explaining why exercise has these positive health benefits are not completely understood. However, developing research suggests that many of the benefits of exercise may come about because of the role of skeletal muscles as endocrine organs. Contracting muscles release hormones called , which promote tissue repair and the growth of new tissue. Myokines also have anti-inflammatory effects, which, in turn, reduce the risk of developing inflammatory diseases. Exercise also reduces levels of , the adrenal cortex stress hormone that may cause many health problems — both physical and mental — at sustained high levels.
Cardiovascular Benefits of Physical Exercise
The beneficial effects of exercise on the cardiovascular system are well documented. Physical inactivity has been identified as a risk factor for the development of coronary artery disease. There is also a direct correlation between physical inactivity and cardiovascular disease mortality. Physical exercise, in contrast, has been demonstrated to reduce several risk factors for cardiovascular disease, including (high blood pressure), “bad” cholesterol (low-density lipoproteins), high total cholesterol, and excess body weight. Physical exercise has also been shown to increase “good” cholesterol (high-density lipoproteins), insulin sensitivity, the mechanical efficiency of the heart, and exercise tolerance, which is the ability to perform physical activity without undue stress and fatigue.
Cognitive Benefits of Physical Exercise
Physical exercise has been shown to help protect people from developing , such as dementia. A 30-year study of almost 2,400 men found that those who exercised regularly had a 59 per cent reduction in when compared with those who did not exercise. Similarly, a review of cognitive enrichment therapies for the elderly found that physical activity — in particular, aerobic exercise — can enhance the cognitive function of older adults. Anecdotal evidence suggests that frequent exercise may even help reverse alcohol-induced brain damage. There are several possible reasons why exercise is so beneficial for the brain. Physical exercise:
- Increases blood flow and oxygen availability to the brain.
- Increases growth factors that promote new brain cells and new neuronal pathways in the brain.
- Increases levels of neurotransmitters (such as serotonin), which increase memory retention, information processing, and cognition.
Mental Health Benefits of Physical Exercise
Numerous studies suggest that regular works as well as pharmaceutical antidepressants in treating mild-to-moderate . A possible reason for this effect is that exercise increases the biosynthesis of at least three that may act as . The euphoric effect of exercise is well known. Distance runners may refer to it as “runner’s high,” and people who participate in crew (as in Figure 12.5.5) may refer to it as “rower’s high.” Because of these effects, health care providers often promote the use of aerobic exercise as a treatment for depression.
Additional mental health benefits of physical exercise include reducing stress, improving body image, and promoting positive self-esteem. Conversely, there is evidence to suggest that being sedentary is associated with increased risk of anxiety.
Sleep Benefits of Physical Exercise
A recent review of published scientific research suggests that exercise generally improves sleep for most people, and helps sleep disorders, such as . In fact, exercise is the most recommended alternative to sleeping pills for people with insomnia. For sleep benefits, the optimum time to exercise may be four to eight hours before bedtime, although exercise at any time of day seems to be beneficial. The only possible exception is heavy exercise undertaken shortly before bedtime, which may actually interfere with sleep.
Other Benefits of Physical Exercise
Some studies suggest that physical activity may benefit the immune systemno post. For example, moderate exercise has been found to be associated with a decreased incidence of upper respiratory tract infections. Evidence from many studies has found a correlation between physical exercise and reduced death rates from , specifically breast cancer and colon cancer. Physical exercise has also been shown to reduce the risk of and .
Variation in Responses to Physical Exercise
Not everyone benefits equally from physical exercise. When participating in , most people will have a moderate increase in their endurance, but some people will as much as double their endurance. Some people, on the other hand, will show little or no increase in endurance from aerobic exercise. Genetic differences in and skeletal muscle fibres may play a role in these different results. People with more slow-twitch fibres may be able to develop greater endurance, because these muscle fibres have more capillaries, , and than fast-twitch fibres. As a result, slow-twitch fibres can carry more oxygen and sustain aerobic activity for a longer period of time than fast-twitch fibres. Studies show that endurance athletes (like the marathoner pictured in Figure 12.5.6) generally do tend to have a higher proportion of slow-twitch fibres than other people.
There is also great variation in individual responses to muscle building as a result of anaerobic exercise. Some people have a much greater capacity to increase muscle size and strength, whereas other people never develop large muscles, no matter how much they exercise them. People who have more fast-twitch than slow-twitch muscle fibres may be able to develop bigger, stronger muscles, because fast-twitch muscle fibres contribute more to muscle strength and have greater potential to increase in mass. Evidence suggests that athletes who excel at power activities (such as throwing and jumping) tend to have a higher proportion of fast-twitch fibres than do endurance athletes.
Can You “Overdose” on Physical Exercise?
Is it possible to exercise too much? Can too much exercise be harmful? Evidence suggests that some adverse effects may occur if exercise is extremely intense and the body is not given proper rest between exercise sessions. Athletes who train for multiple marathons have been shown to develop scarring of the heart and heart rhythm abnormalities. Doing too much exercise without prior conditioning also increases the risk of injuries to muscles and joints. Damage to muscles due to overexertion is often seen in new military recruits (see Figure 12.5.7). Too much exercise in females may cause amenorrhea, which is a cessation of menstrual periods. When this occurs, it generally indicates that a woman is pushing her body too hard.
Many people develop delayed onset muscle soreness (DOMS), which is pain or discomfort in muscles that is felt one to three days after exercising, and generally subsides two or three days later. DOMS was once thought to be caused by the buildup of lactic acid in the muscles. Lactic acid is a product of in muscle tissues. However, lactic acid disperses fairly rapidly, so it is unlikely to explain pain experienced several days after exercise. The current theory is that DOMS is caused by tiny tears in muscle fibres, which occur when muscles are used at too high a level of intensity.
Feature: My Human Body
Most people know that exercise is important for good health, and it’s easy to find endless advice about exercise programs and fitness plans. What is not so easy to find is the motivation to start exercising — and to stick with it. This is the main reason why so many people fail to get regular exercise. Practical concerns like a busy schedule and bad weather can certainly make exercising more of a challenge, but the biggest barriers to adopting a regular exercise routine are mental. If you want to exercise but find yourself making excuses or getting discouraged and giving up, here are some tips that may help you get started and stay moving:
- Avoid an all-or-nothing point of view. Don’t think you need to spend hours sweating at the gym or training for a marathon to get healthy. Even a little bit of exercise is better than nothing at all. Start out with ten or 15 minutes of moderate activity each day. Taking a walk around your neighborhood is a great way to begin! From there, gradually increase the amount of time until you are exercising to at least 30 minutes a day, five days a week. Make it a routine.
- Be kind to yourself, and reinforce positive behaviors with rewards. Don’t be down on yourself because you are overweight or out of shape. Don’t beat yourself up because of a supposed lack of willpower. Instead, look at any past failures as opportunities to learn and do better. When you do achieve even small exercise goals, treat yourself to something special. Did you just complete your first workout? Reward yourself with a relaxing bath or other treat.
- Don’t make excuses for not exercising. Common complaints include being too busy or tired or not athletic enough. Such excuses are not valid reasons to avoid exercising, and they will sabotage any plans to improve your fitness. If you can’t find a 30-minute period to work out, try to find ten minutes, three times a day. If you’re feeling tired, know that exercise can actually reduce fatigue and boost your energy level. If you feel clumsy and uncoordinated, remind yourself that you don’t need to be athletic to take a walk or engage in vigorous house or yard work.
- Find an activity that you truly enjoy doing. Don’t think you have to lift weights or run on a treadmill to exercise your muscles. If you find such activities boring or unpleasant, you won’t stick with them. Any activity that increases your heart rate and uses large muscles can provide a workout, especially if you’re not in the habit of exercising, so find something you like to do. Do you like to dance? Put on some music and dance up a sweat! Do you enjoy gardening? Get out in the yard and dig up some dirt! Still not interested? Try an activity-based video game, such as Wii or Kinect. You may find it so much fun that it doesn’t seem like exercise until you realize you’ve worked up a sweat.
- Make yourself accountable. Tell friends and family members that you’re going to start exercising. You’ll be letting them — as well as yourself — down if you don’t follow through. Some people find that keeping an exercise log to track their progress is a good way to be accountable and stick to an exercise program. Perhaps the best way to keep at it is to find an exercise partner. If you’ve got someone waiting to exercise with you, you will be less likely to make excuses for not exercising.
- Add more physical activity to your daily life. You don’t need to follow a structured exercise program to increase your activity level. Do your house or yard work briskly for a workout. Park your car further than necessary from work or the mall, and walk the extra distance. If you live close enough, leave the car at home and walk to and from your destination. Rather than taking elevators or escalators, walk up and down stairs. When you take breaks at work, take a walk instead of sitting. Every time a commercial comes on while you’re watching TV, take a quick exercise break — run in place or do some curls with hand weights.
12.5 Summary
- is any bodily activity that enhances or maintains physical fitness and overall health. Activities such as household chores may count as physical exercise, even if they are not done for their health benefits. Current recommendations for adults are 30 minutes a day of moderate exercise.
- is any physical activity that uses muscles at less than their maximum contraction strength, but for long periods of time. This type of exercise uses a relatively high percentage of that consume large amounts of oxygen. Aerobic exercises increase cardiovascular endurance and include cycling and brisk walking.
- is any physical activity that uses muscles at close to their maximum contraction strength, but for short periods of time. This type of exercise uses a relatively high percentage of that consume small amounts of oxygen. Anaerobic exercises increase muscle and bone mass and strength, and they include push-ups and sprinting.
- is any physical activity that stretches and lengthens muscles, thereby improving range of motion and reducing risk of injury. Examples include stretching and yoga.
- Many studies have shown that physical exercise is positively correlated with a diversity of physical, mental, and emotional health benefits. Physical exercise also increases quality of life and life expectancy.
- Many of the benefits of exercise may come about because contracting muscles release hormones called , which promote tissue repair and growth and have anti-inflammatory effects.
- Physical exercise can reduce risk factors for cardiovascular disease, including hypertension and excess body weight. Physical exercise can also increase factors associated with cardiovascular health, such as mechanical efficiency of the heart.
- Physical exercise has been shown to offer protection from and other cognitive problems, perhaps because it increases blood flow or in the , among other potential effects.
- Numerous studies suggest that regular aerobic exercise works as well as pharmaceutical antidepressants in treating mild-to-moderate depression, possibly because it increases synthesis of natural euphoriants in the brain.
- Research shows that physical exercise generally improves sleep for most people and helps sleep disorders, such as insomnia. Other health benefits of physical exercise include better immune system function and reduced risk of type 2 diabetes and obesity.
- There is great variation in individual responses to exercise, partly due to genetic differences in proportions of slow-twitch and fast-twitch skeletal muscle fibres. People with more slow-twitch fibres may be able to develop greater endurance from aerobic exercise, whereas people with more fast-twitch fibres may be able to develop greater muscle size and strength from anaerobic exercise.
- Some adverse effects may occur if exercise is extremely intense and the body is not given proper rest between exercise sessions. Many people who overwork their muscles develop delayed onset muscle soreness (DOMS), which may be caused by tiny tears in muscle fibres.
12.5 Review Questions
- How do we define physical exercise?
- What are current recommendations for physical exercise for adults?
- Define flexibility exercise, and state its benefits. What are two examples of flexibility exercises?
- In general, how does physical exercise affect health, quality of life, and longevity?
- What mechanism may underlie many of the general health benefits of physical exercise?
- Relate physical exercise to cardiovascular disease risk.
- What may explain the positive benefits of physical exercise on cognition?
- How does physical exercise compare with antidepressant drugs in the treatment of depression?
- Identify several other health benefits of physical exercise.
- Explain how genetics may influence the way individuals respond to physical exercise.
- Can too much physical exercise be harmful?
12.5 Explore More
How playing sports benefits your body … and your brain – Leah Lagos and Jaspal Ricky Singh, TED-Ed, 2016.
The surprising reason our muscles get tired – Christian Moro, TED-Ed, 2019.
What makes muscles grow? – Jeffrey Siegel, TED-Ed, 2015.
Why some people find exercise harder than others | Emily Balcetis, TED, 2014.
Attributions
Figure 12.5.1
stroller fit by Serge Melki from Indianapolis, USA on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 12.5.2
Children kayaking young sport by Hagerty Ryan, USFWS on Pixnio is used under a public domain (CC0) Certification (https://creativecommons.org/licenses/publicdomain/).
Figure 12.5.3
Bicep curls [photo] by Senior Airman Jarrod Grammel from U.S. Moody Air Force Base is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 12.5.4
Flexibility exercise by carl-barcelo-nqUHQkuVj3c [photo] by Carl Barcelo on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 12.5.5
Canadian women’s double scull silver Rio 2016 by Gerhard Pratt on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 12.5.6
Toronto Marathon 2012 by Marc Roberts on Flickr is used under a CC BY-NC-SA 2.0 (https://creativecommons.org/licenses/by-nc-sa/2.0/) license.
Figure 12.5.7
Muscle damage in military recruits by Lance Cpl. Bridget M. Keane from the United States Marine Corps Recruit Depot is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Elwood, P., Galante, J., Pickering, J., Palmer, S., Bayer, A., Ben-Shlomo, Y., Longley, M., & Gallacher, J. (2013). Healthy lifestyles reduce the incidence of chronic diseases and dementia: evidence from the Caerphilly cohort study. PloS one, 8(12), e81877. https://doi.org/10.1371/journal.pone.0081877
Mayo Clinic Staff. (n.d.). Amenorrhea [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/amenorrhea/symptoms-causes/syc-20369299#
Mayo Clinic Staff. (n.d.). Coronary artery disease [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/coronary-artery-disease/symptoms-causes/syc-20350613
TED-Ed. (2016, June 28). How playing sports benefits your body … and your brain – Leah Lagos and Jaspal Ricky Singh. YouTube. https://www.youtube.com/watch?v=hmFQqjMF_f0&feature=youtu.be
TED-Ed. (2019, April 18). The surprising reason our muscles get tired – Christian Moro. YouTube. https://www.youtube.com/watch?v=rLsimrBoYXc&feature=youtu.be
TED-Ed. (2015, November 3). What makes muscles grow? – Jeffrey Siegel. YouTube https://www.youtube.com/watch?v=2tM1LFFxeKg&feature=youtu.be
TED. (2014, November 14). Why some people find exercise harder than others | Emily Balcetis, YouTube. https://www.youtube.com/watch?v=QeIrdqU0o9s&feature=youtu.be
Wikipedia contributors. (2020, August 1). Delayed onset muscle soreness. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Delayed_onset_muscle_soreness&oldid=970682631
Created by CK-12 Foundation/Adapted by Christine Miller
Case Study Conclusion: Drink and Flush
You are probably aware that, because of its effects on the brain, drinking alcohol can cause visual disturbances, slurred speech, drowsiness, impaired judgment, and loss of coordination. Although it may be less obvious, alcohol also can have serious effects on the functioning of the excretory system.
As you learned from the conversation between Talia and Shae — who were in line for the restroom at the beginning of this chapter — alcohol consumption inhibits a hormone that causes our bodies to retain water. As a result, more water is released in urine, increasing the frequency of restroom trips, as well as the risk of dehydration.
Which hormone discussed in this chapter does this? If you answered (ADH; also called vasopressin) — you are correct! ADH is secreted by the posterior and acts on the . As you have learned, the kidneys filter the blood, reabsorb needed substances, and produce . ADH helps the body conserve water by influencing this process. ADH makes the collecting ducts in the kidneys permeable to water, allowing water molecules to be reabsorbed from the urine back into the blood through osmosis into capillaries.
Alcohol is thought to produce more dilute urine by inhibiting the release of ADH. This causes the to be more impermeable to water, so less water can be reabsorbed, and more is excreted in urine. Because the volume of urine is increased, the bladder fills up more quickly, and the urge to urinate occurs more frequently. This is part of the reason why you often see a long line for the restroom in situations where many people are drinking alcohol. In addition to producing more dilute urine, simply consuming many beverages can also increase urine output.
In most cases, moderate drinking causes only a minor and temporary effect on kidney function. However, when people consume a large quantity of alcohol in a short period of time, or abuse alcohol over long time periods, there can be serious effects on the kidney. Binge drinking (consuming roughly four to five drinks in two hours) can cause a condition called “acute kidney injury,” a serious and sudden impairment of kidney function that requires immediate medical attention. As with the other cases of kidney failure that you learned about in this chapter, the treatment is to artificially filter the blood using . While normal kidney function may eventually return, acute kidney injury can sometimes cause long-term damage to the kidneys.
In cases where people abuse alcohol, particularly for an extended period of time, there can be many serious effects on the kidneys and other parts of the excretory system. The dehydrating effect of alcohol on the body can impair the function of many organs, including the kidneys themselves. Additionally, because of alcohol’s effect on kidney function, water balance, and ion balance, chronic alcohol consumption can cause abnormalities in blood ion concentration and acid-base balance, which can be very dangerous.
Drinking more than two alcoholic beverages a day can increase your risk for high blood pressure, too. As you have learned, high blood pressure is a risk factor for some kidney disorders, as well as a common cause of . Drinking too much alcohol can damage the kidneys by raising blood pressure.
Finally, chronic excessive consumption of alcohol can cause liver disease. The liver is an important organ of the that breaks down toxic substances in the blood. The liver and kidneys work together to remove wastes from the bloodstream. You may remember, for example, the liver transforms into , which is then filtered and excreted by the kidneys. When the liver is not functioning normally, it puts added strain on the kidneys, which can result in kidney dysfunction. This association between alcohol, liver disease, and kidney dysfunction is so strong that most of the patients in Canada with both liver disease and related kidney dysfunction are alcoholics.
As you have learned, the excretory system is essential in removing toxic wastes from the body and regulating homeostasis. Having an occasional drink can temporarily alter these functions, but excessive alcohol exposure can seriously and permanently damage this system in many ways. Limiting alcohol consumption can help preserve the normal functioning of the excretory system, so that it can protect your health.
Chapter 16 Summary
In this chapter you learned about the excretory system. Specifically, you learned that:
- 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 in which the human body maintains .
- Organs of the excretory system include the skin, liver, large intestine, lungs, and kidneys.
-
- The plays a role in excretion through the production of by sweat glands. Sweating eliminates excess water and salts, as well as a small amount of , a byproduct of protein .
- The is a very important organ of excretion. The liver breaks down many substances — including toxins — in the blood. The liver also excretes (a waste product of hemoglobin catabolism) in bile. then travels to the small intestine and is eventually excreted in by the large intestine.
- The main excretory function of the 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.
- 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 . The kidneys filter many substances out of blood, allow the blood to reabsorb needed materials, and use the remaining materials to form urine.
-
- 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 — which are the tiny functional units of the kidney — span the and . 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 and the surrounding form the unit that filters blood. From the glomerular capsule, the material filtered from blood (called filtrate) passes through the long . 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 are part of the urinary system, which also includes the , , and . The main function of the urinary system is to eliminate the waste products of metabolism from the body by forming and excreting urine. After urine forms in the kidneys, it is transported through the ureters to the bladder. The bladder stores the urine until urination, when urine is transported by the urethra to be excreted outside the body.
-
- Besides the elimination of waste products such as urea, uric acid, excess water, and mineral ions, the urinary system has other vital functions. These include maintaining of mineral ions in extracellular fluid, regulating acid-base balance in the blood, regulating the volume of extracellular fluids, and controlling blood pressure.
-
-
- The formation of urine must be closely regulated to maintain body-wide homeostasis. Several endocrine hormones help control this function of the urinary system, including secreted from the posterior pituitary gland, from the parathyroid glands, and from the adrenal glands.
-
-
-
-
- For example, the kidneys 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 — which helps control the level of calcium in the blood — and , which stimulates bone marrow to produce red blood cells.
-
- The process of urination is controlled by both the autonomic and the somatic nervous systems. The causes the detrusor muscle in the bladder wall to relax as the bladder fills with urine, but conscious contraction of the detrusor muscle expels urine from the bladder during urination.
- Ureters are tube-like structures that connect the kidneys with the urinary bladder. Each ureter arises at the of a kidney and travels down through the abdomen to the urinary bladder. The walls of the ureter contain that can contract to push urine through the ureter by . The walls are lined with transitional epithelium that can expand and stretch.
- The urinary bladder is a hollow, muscular organ that rests on the pelvic floor. It is also lined with transitional epithelium. The function of the bladder is to collect and store urine from the kidneys before the urine is eliminated through urination. Filling of the bladder triggers the autonomic nervous system to stimulate the detrusor muscle in the bladder wall to contract. This forces urine out of the bladder and into the urethra.
- The urethra is a tube that connects the urinary bladder to the external urethral orifice. Somatic nerves control the at the distal end of the urethra. This allows the opening of the sphincter for urination to be under voluntary control.
-
- is a progressive kidney disease caused by damage to the capillaries in the glomeruli of the kidneys due to long-standing diabetes mellitus. Years of capillary damage may occur before symptoms first appear.
- (PKD) is a genetic disorder (autosomal dominant or recessive) in which multiple abnormal cysts grow in the kidneys.
- Diabetic nephropathy, PKD, or chronic hypertension may lead to kidney failure, in which the kidneys are no longer able to adequately filter metabolic wastes from the blood. Kidneys may fail to such a degree that kidney transplantation or repeated, frequent is needed to support life. In hemodialysis, the patient’s blood is filtered artificially through a machine and then returned to the patient’s circulation.
- A kidney stone is a solid crystal that forms in a kidney from minerals in urine. A small stone may pass undetected through the ureters and the rest of the urinary tract. A larger stone may cause pain when it passes or be too large to pass, causing blockage of a ureter. Large kidney stones may be shattered with high-intensity ultrasound into pieces small enough to pass through the urinary tract, or they may be removed surgically.
- A bladder infection is generally caused by bacteria that reach the bladder from the GI tract and multiply. Bladder infections are much more common in females than males because the female urethra is much shorter and closer to the anus. Treatment generally includes antibiotic drugs.
- Urinary incontinence is a chronic problem of uncontrolled leakage of urine. It is very common, especially at older ages and in women. In men, urinary incontinence is usually caused by an enlarged prostate gland. In women, it is usually caused by stretching of pelvic floor muscles during childbirth (stress incontinence) or by an “overactive bladder” that empties without warning (urge incontinence).
You have learned that, through the removal of toxic wastes and the maintenance of homeostasis, the excretory system protects your body. But how does your body protect itself against pathogens and other threats? Read the next chapter on the immune system to find out.
Chapter 16 Review
- In what ways can the alveoli of the lungs be considered analogous to the nephrons of the kidney?
- What is urea? Where is urea produced, and what is it produced from? How is urea excreted from the body?
- If a person has a large kidney stone preventing urine that has left the kidney from reaching the bladder, where do you think this kidney stone is located? Explain your answer.
- As it relates to urine production, explain what is meant by “Excretion = Filtration – Reabsorption + Secretion."
- Which disease discussed in the chapter specifically affects the glomerular capillaries of the kidneys? Where are the glomerular capillaries located within the kidneys, and what is their function?
- Describe one way in which the excretory system helps maintain homeostasis in the body.
- High blood pressure can both contribute to the development of kidney disorders and be a symptom of kidney disorders. What is a kidney disorder that can be caused by high blood pressure? What is a kidney disorder that has high blood pressure as a symptom? How does blood pressure generally relate to the function of the kidney?
- If the body is dehydrated, what do the kidneys do? What does this do to the appearance of the urine produced?
- Identify three risk factors for the development of kidney stones.
Attribution
Figure 16.7.1
Tags: Alcohol Drink Alkolismus Bottles Glass Container by Gerd Altmann [geralt] on Pixabay is used under the Pixabay License (https://pixabay.com/service/license/).
Created by CK-12 Foundation/Adapted by Christine Miller
Worm Attack!
Does the organism in Figure 17.2.1 look like a space alien? A scary creature from a nightmare? In fact, it’s a 1-cm long worm in the genus Schistosoma. It may invade and take up residence in the human body, causing a very serious illness known as . The worm gains access to the human body while it is in a microscopic life stage. It enters through a hair follicle when the skin comes into contact with contaminated water. The worm then grows and matures inside the human organism, causing disease.
Host vs. Pathogen
The Schistosoma worm has a parasitic relationship with humans. In this type of relationship, one organism, called the , lives on or in another organism, called the host. The parasite always benefits from the relationship, and the host is always harmed. The human host of the Schistosoma worm is clearly harmed by the parasite when it invades the host’s tissues. The urinary tract or intestines may be infected, and signs and symptoms may include abdominal pain, diarrhea, bloody stool, or blood in the urine. Those who have been infected for a long time may experience damage, , , or bladder . In children, Schistosoma infection may cause poor growth and difficulty learning.
Like the Schistosoma worm, many other organisms can make us sick if they manage to enter our body. Any such agent that can cause disease is called a . Most pathogens are , although some — such as the Schistosoma worm — are much larger. In addition to worms, common types of pathogens of human hosts include , es, fungi, and single-celled organisms called protists. You can see examples of each of these types of pathogens in Table 17.1.1. Fortunately for us, our immune system is able to keep most potential pathogens out of the body, or quickly destroy them if they do manage to get in. When you read this chapter, you’ll learn how your immune system usually keeps you safe from harm — including from scary creatures like the Schistosoma worm!
Type of Pathogen | Description | Disease Caused | |
---|---|---|---|
Bacteria:
Example shown: Escherichia coli |
Single celled organisms without a nucleus | Strep throat, staph infections, tuberculosis, food poisoning, tetanus, pneumonia, syphillis | |
Viruses:
Example shown: Herpes simplex |
Non-living particles that reproduce by taking over living cells | Common cold, flu, genital herpes, cold sores, measles, AIDS, genital warts, chicken pox, small pox | |
Fungi:
Example shown: Death cap mushroom |
Simple organisms, including mushrooms and yeast, that grow as single cells or thread-like filaments | Ringworm, athletes foot, tineas, candidias, histoplasmomis, mushroom poisoning | |
Protozoa:
Example shown: Giardia lamblia |
Single celled organisms with a nucleus | Malaria, "traveller's diarrhea", giardiasis, typano somiasis ("sleeping sickness") |
What is the Immune System?
The immune systemno post is a host defense system. It comprises many biological structures —ranging from individual leukocytes to entire organs — as well as many complex biological processes. The function of the immune system is to protect the host from pathogens and other causes of disease, such as tumor (cancer) cells. To function properly, the immune system must be able to detect a wide variety of pathogens. It also must be able to distinguish the cells of pathogens from the host’s own cells, and also to distinguish cancerous or damaged host cells from healthy cells. In humans and most other vertebrates, the immune system consists of layered defenses that have increasing specificity for particular pathogens or tumor cells. The layered defenses of the human immune system are usually classified into two subsystems, called the innate immune system and the adaptive immune system.
Innate Immune System
The (sometimes referred to as "non-specific defense") provides very quick, but non-specific responses to pathogens. It responds the same way regardless of the type of pathogen that is attacking the host. It includes barriers — such as the skin and mucous membranes — that normally keep pathogens out of the body. It also includes general responses to pathogens that manage to breach these barriers, including chemicals and cells that attack the pathogens inside the human host. Certain leukocytes (white blood cells), for example, engulf and destroy pathogens they encounter in the process called , which is illustrated in Figure 17.2.2. Exposure to pathogens leads to an immediate maximal response from the innate immune system.
Watch the video below, "Neutrophil Phagocytosis - White Blood Cells Eats Staphylococcus Aureus Bacteria" by ImmiflexImmuneSystem, to see phagocytosis in action.
https://youtu.be/Z_mXDvZQ6dU
Neutrophil Phagocytosis - White Blood Cell Eats Staphylococcus Aureus Bacteria, ImmiflexImmuneSystem, 2013.
Adaptive Immune System
The is activated if pathogens successfully enter the body and manage to evade the general defenses of the innate immune system. An adaptive response is specific to the particular type of pathogen that has invaded the body, or to cancerous cells. It takes longer to launch a specific attack, but once it is underway, its specificity makes it very effective. An adaptive response also usually leads to immunity. This is a state of resistance to a specific pathogen, due to the adaptive immune system's ability to “remember” the pathogen and immediately mount a strong attack tailored to that particular pathogen if it invades again in the future.
Self vs. Non-Self
Both innate and adaptive immune responses depend on the immune system's ability to distinguish between self- and non-self molecules. are those components of an organism’s body that can be distinguished from foreign substances by the immune system. Virtually all body cells have surface proteins that are part of a complex called . These proteins are one way the immune system recognizes body cells as self. , in contrast, are recognized as foreign, because they are different from self proteins.
Antigens and Antibodies
Many non-self molecules comprise a class of compounds called antigens. s, which are usually proteins, bind to specific receptors on immune system cells and elicit an adaptive immune response. Some adaptive immune system cells (B cells) respond to foreign antigens by producing antibodies. An is a molecule that precisely matches and binds to a specific antigen. This may target the antigen (and the pathogen displaying it) for destruction by other immune cells.
Antigens on the surface of pathogens are how the recognizes specific pathogens. Antigen specificity allows for the generation of responses tailored to the specific pathogen. It is also how the adaptive immune system ”remembers” the same pathogen in the future.
Immune Surveillance
Another important role of the immune system is to identify and eliminate tumor cells. This is called . The transformed cells of tumors express antigens that are not found on normal body cells. The main response of the immune system to tumor cells is to destroy them. This is carried out primarily by aptly-named killer T cells of the adaptive immune system.
Lymphatic System
The is a human organ system that is a vital part of the adaptive immune system. It is also part of the and plays a major role in the (see section 17.3 Lymphatic System). The major structures of the lymphatic system are shown in Figure 17.2.3 .
The lymphatic system consists of several lymphatic organs and a body-wide network of lymphatic vessels that transport the fluid called lymph. is essentially blood plasma that has leaked from into tissue spaces. It includes many leukocytes, especially , which are the major cells of the lymphatic system. Like other leukocytes, lymphocytes defend the body. There are several different types of lymphocytes that fight pathogens or cancer cells as part of the adaptive immune system.
Major lymphatic organs include the and . Their function is to form and/or mature lymphocytes. Other lymphatic organs include the , , and , which are small clumps of lymphoid tissue clustered along lymphatic vessels. These other lymphatic organs harbor mature lymphocytes and filter lymph. They are sites where pathogens collect, and adaptive immune responses generally begin.
Neuroimmune System vs. Peripheral Immune System
The and are normally protected from pathogens in the blood by the selectively permeable blood-brain and blood-spinal cord barriers. These barriers are part of the . The neuroimmune system has traditionally been considered distinct from the rest of the immune system, which is called the — although that view may be changing. Unlike the peripheral system, in which leukocytes are the main cells, the main cells of the neuroimmune system are thought to be nervous system cells called . These cells can recognize and respond to pathogens, debris, and other potential dangers. Types of neuroglia involved in neuroimmune responses include microglial cells and astrocytes.
- are among the most prominent types of neuroglia in the brain. One of their main functions is to phagocytize cellular debris that remains when neurons die. Microglial cells also “prune” obsolete synapses between neurons.
- are neuroglia that have a different immune function. They allow certain immune cells from the peripheral immune system to cross into the brain via the blood-brain barrier to target both pathogens and damaged nervous tissue.
Feature: Human Biology in the News
“They’ll have to rewrite the textbooks!”
That sort of response to a scientific discovery is sure to attract media attention, and it did. It’s what Kevin Lee, a neuroscientist at the University of Virginia, said in 2016 when his colleagues told him they had discovered human anatomical structures that had never before been detected. The structures were tiny lymphatic vessels in the meningeal layers surrounding the brain.
How these lymphatic vessels could have gone unnoticed when all human body systems have been studied so completely is amazing in its own right. The suggested implications of the discovery are equally amazing:
- The presence of these lymphatic vessels means that the brain is directly connected to the , presumably allowing a close association between the human brain and human pathogens. This suggests an entirely new avenue by which humans and their pathogens may have influenced each other’s evolution. The researchers speculate that our pathogens even may have influenced the evolution of our social behaviors.
- The researchers think there will also be many medical applications of their discovery. For example, the newly discovered lymphatic vessels may play a major role in neurological diseases that have an immune component, such as multiple sclerosis. The discovery might also affect how conditions such as autism spectrum disorders and schizophrenia are treated.
17.2 Summary
- Any agent that can cause disease is called a . Most human pathogens are , such as and . The immune system is the body system that defends the human host from pathogens and cancerous cells.
- The is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that pathogens, and several other general responses.
- The is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to immunity to the pathogens.
- Both innate and adaptive immune responses depend on the immune system's ability to distinguish between self and non-self molecules. Most body cells have proteins that identify them as self. Pathogens and tumor cells have non-self antigens that the immune system recognizes as foreign.
- are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Generally, they are non-self molecules on pathogens or infected cells. Some immune cells (B cells) respond to foreign antigens by producing that bind with antigens and target pathogens for destruction.
- Tumor surveillance is an important role of the immune system. Killer T cells of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.
- The lymphatic system is a human organ system vital to the adaptive immune system. It consists of several organs and a system of vessels that transport lymph. The main immune function of the lymphatic system is to produce, mature, and circulate lymphocytes, which are the main cells in the adaptive immune system.
- The neuroimmune system that protects the central nervous system is thought to be distinct from the peripheral immune system that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection for the neuroimmune system. Neuroglia also play role in this system, for example, by carrying out phagocytosis.
17.2 Review Questions
- What is a pathogen?
- State the purpose of the immune system.
- Compare and contrast the innate and adaptive immune systems.
- Explain how the immune system distinguishes self molecules from non-self molecules.
- What are antigens?
- Define tumor surveillance.
- Briefly describe the lymphatic system and its role in immune function.
- Identify the neuroimmune system.
- What does it mean that the immune system is not just composed of organs?
- Why is the immune system considered “layered?”
17.2 Explore More
https://youtu.be/xZbcwi7SfZE
The Antibiotic Apocalypse Explained, Kurzgesagt – In a Nutshell, 2016.
https://youtu.be/Nw27_jMWw10
Overview of the Immune System, Handwritten Tutorials, 2011.
https://youtu.be/gVdY9KXF_Sg
The surprising reason you feel awful when you're sick - Marco A. Sotomayor, TED-Ed, 2016.
Attributions
Figure 17.1.1
Schistosome Parasite by Bruce Wetzel and Harry Schaefer (Photographers) from the National Cancer Institute, Visuals online is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 17.1.2
Phagocytosis by Rlawson at en.wikibooks on Wikimedia Commons is used under a CC BY SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. (Transferred from en.wikibooks to Commons by User:Adrignola.)
Figure 17.1.3
2201_Anatomy_of_the_Lymphatic_System by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Table 17.1.1
- EscherichiaColi NIAID [photo] by Rocky Mountain Laboratories, NIH National Institute of Allergy and Infectious Diseases (NIAID) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
- Herpes simplex virus TEM B82-0474 lores by Dr. Erskine Palmer/ CDC Public Health Image Library (PHIL) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
- Red death cap mushroom by Rosendahl on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Transferred from Pixnio by Fæ.)
- Scanning electron micrograph (SEM) of Giardia lamblia by Janice Haney Carr/ CDC, Public Health Image Library (PHIL) Photo ID# 8698 is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Barney, J. (2016, March 21). They’ll have to rewrite the textbooks [online article]. Illimitable - Discovery. UVA Today/ University of Virginia. https://news.virginia.edu/illimitable/discovery/theyll-have-rewrite-textbooks
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 21.2 Anatomy of the lymphatic system [digital image]. In Anatomy and Physiology (Section 21.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/21-1-anatomy-of-the-lymphatic-and-immune-systems
Handwritten Tutorials. (2011, October 25). Overview of the immune system. YouTube. https://www.youtube.com/watch?v=Nw27_jMWw10&feature=youtu.be
ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis - White blood cell eats staphylococcus aureus bacteria. YouTube. https://www.youtube.com/watch?v=Z_mXDvZQ6dU
Kurzgesagt – In a Nutshell. (2016, March 16). The antibiotic apocalypse explained. YouTube. https://www.youtube.com/watch?v=xZbcwi7SfZE&feature=youtu.be
Louveau, A., Smirnov, I., Keyes, T. J., Eccles, J. D., Rouhani, S. J., Peske, J. D., Derecki, N. C., Castle, D., Mandell, J. W., Lee, K. S., Harris, T. H., & Kipnis, J. (2015). Structural and functional features of central nervous system lymphatic vessels. Nature, 523(7560), 337–341. https://doi.org/10.1038/nature14432
Mayo Clinic Staff. (n.d.). Autism spectrum disorder [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/autism-spectrum-disorder/symptoms-causes/syc-20352928
Mayo Clinic Staff. (n.d.). Multiple sclerosis [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/multiple-sclerosis/symptoms-causes/syc-20350269
Mayo Clinic Staff. (n.d.). Schizophrenia [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/schizophrenia/symptoms-causes/syc-20354443
TED-Ed. (2016, April 19). The surprising reason you feel awful when you're sick - Marco A. Sotomayor. YouTube. https://www.youtube.com/watch?v=gVdY9KXF_Sg&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Tonsillitis
The white patches on either side of the throat in Figure 17.3.1 are signs of tonsillitis. The tonsils are small structures in the throat that are very common sites of infection. The white spots on the tonsils pictured here are evidence of infection. The patches consist of large amounts of dead bacteria, cellular debris, and white blood cells — in a word: pus. Children with recurrent tonsillitis may have their tonsils removed surgically to eliminate this type of infection. The tonsils are organs of the lymphatic system.
What Is the Lymphatic System?
The is a collection of organs involved in the production, maturation, and harboring of white blood cells called lymphocytes. It also includes a network of vessels that transport or filter the fluid known as in which lymphocytes circulate. Figure 17.3.2 shows major lymphatic vessels and other structures that make up the lymphatic system. Besides the tonsils, organs of the lymphatic system include the thymus, the spleen, and hundreds of lymph nodes distributed along the lymphatic vessels.
The lymphatic vessels form a transportation network similar in many respects to the of the . However, unlike the cardiovascular system, the lymphatic system is not a closed system. Instead, lymphatic vessels carry lymph in a single direction — always toward the upper chest, where the lymph empties from lymphatic vessels into blood vessels.
Cardiovascular Function of the Lymphatic System
The return of lymph to the bloodstream is one of the major functions of the lymphatic system. When blood travels through of the cardiovascular system, it is under pressure, which forces some of the components of blood (such as water, oxygen, and nutrients) through the walls of the capillaries and into the tissue spaces between cells, forming tissue fluid, also called interstitial fluid (see Figure 17.3.3). Interstitial fluid bathes and nourishes cells, and also absorbs their waste products. Much of the water from interstitial fluid is reabsorbed into the capillary blood by osmosis. Most of the remaining fluid is absorbed by tiny lymphatic vessels called lymph capillaries. Once interstitial fluid enters the lymphatic vessels, it is called lymph. Lymph is very similar in composition to blood plasma. Besides water, lymph may contain proteins, waste products, cellular debris, and pathogens. It also contains numerous white blood cells, especially the subset of white blood cells known as lymphocytes. In fact, lymphocytes are the main cellular components of lymph.
The lymph that enters lymph capillaries in tissues is transported through the lymphatic vessel network to two large lymphatic ducts in the upper chest. From there, the lymph flows into two major veins (called subclavian veins) of the cardiovascular system. Unlike blood, lymph is not pumped through its network of vessels. Instead, lymph moves through lymphatic vessels via a combination of contractions of the vessels themselves and the forces applied to the vessels externally by skeletal muscles, similarly to how blood moves through veins. Lymphatic vessels also contain numerous valves that keep lymph flowing in just one direction, thereby preventing backflow.
Digestive Function of the Lymphatic System
Lymphatic vessels called (see Figure 17.3.4) are present in the lining of the gastrointestinal tract, mainly in the small intestine. Each tiny in the lining of the small intestine has an internal bed of capillaries and lacteals. The capillaries absorb most nutrients from the digestion of food into the blood. The lacteals absorb mainly fatty acids from lipid digestion into the lymph, forming a fatty-acid-enriched fluid called . Vessels of the lymphatic network then transport chyle from the to the main lymphatic ducts in the chest, from which it drains into the blood circulation. The nutrients in chyle then circulate in the blood to the liver, where they are processed along with the other nutrients that reach the liver directly via the bloodstream.
Immune Function of the Lymphatic System
The primary immune function of the lymphatic system is to protect the body against pathogens and cancerous cells. This function of the lymphatic system is centred on the production, maturation, and circulation of lymphocytes. s are leukocytes that are involved in the . They are responsible for the recognition of — and tailored defense against — specific pathogens or tumor cells. Lymphocytes may also create a lasting memory of pathogens, so they can be attacked quickly and strongly if they ever invade the body again. In this way, lymphocytes bring about long-lasting immunity to specific pathogens.
There are two major types of lymphocytes, called B cells and T cells. Both B cells and T cells are involved in the adaptive immune response, but they play different roles.
Production and Maturation of Lymphocytes
Like all other types of blood cells (including erythrocytes), both B cells and T cells are produced from stem cells in the red marrow inside bones. After lymphocytes first form, they must go through a complicated maturation process before they are ready to search for pathogens. In this maturation process, they “learn” to distinguish self from non-self. Only those lymphocytes that successfully complete this maturation process go on to actually fight infections by pathogens.
B cells mature in the , which is why they are called B cells. After they mature and leave the bone marrow, they travel first to the circulatory system and then enter the lymphatic system to search for pathogens. T cells, on the other hand, mature in the , which is why they are called T cells. The is illustrated in Figure 17.3.5. It is a small lymphatic organ in the chest that consists of an outer cortex and inner medulla, all surrounded by a fibrous capsule. After maturing in the thymus, T cells enter the rest of the lymphatic system to join B cells in the hunt for pathogens. The bone marrow and thymus are called because of their role in the production and/or maturation of lymphocytes.
Lymphocytes in Secondary Lymphoid Organs
The , , and s are referred to as . These organs do not produce or mature lymphocytes. Instead, they filter lymph and store lymphocytes. It is in these secondary lymphoid organs that pathogens (or their antigens) activate lymphocytes and initiate adaptive immune responses. Activation leads to cloning of pathogen-specific lymphocytes, which then circulate between the lymphatic system and the blood, searching for and destroying their specific pathogens by producing antibodies against them.
Tonsils
There are four pairs of human s. Three of the four are shown in Figure 17.3.6. The fourth pair, called tubal tonsils, is located at the back of the nasopharynx. The palatine tonsils are the tonsils that are visible on either side of the throat. All four pairs of tonsils encircle a part of the anatomy where the respiratory and gastrointestinal tracts intersect, and where pathogens have ready access to the body. This ring of tonsils is called Waldeyer's ring.
Spleen
The (Figure 17.3.7) is the largest of the secondary lymphoid organs, and is centrally located in the body. Besides harboring and filtering , the spleen also filters . Most dead or aged erythrocytes are removed from the blood in the red pulp of the spleen. Lymph is filtered in the white pulp of the spleen. In the fetus, the spleen has the additional function of producing red blood cells. This function is taken over by bone marrow after birth.
Lymph Nodes
Each is a small, but organized collection of lymphoid tissue (see Figure 17.3.8) that contains many lymphocytes. Lymph nodes are located at intervals along the lymphatic vessels, and lymph passes through them on its way back to the blood.
There are at least 500 lymph nodes in the human body. Many of them are clustered at the base of the limbs and in the neck. Figure 17.3.9 shows the major lymph node concentrations, and includes the spleen and the region named Waldeyer’s ring, which consists of the tonsils.
Feature: Myth vs. Reality
When lymph nodes become enlarged and tender to the touch, they are obvious signs of immune system activity. Because it is easy to see and feel swollen lymph nodes, they are one way an individual can monitor his or her own health. To be useful in this way, it is important to know the myths and realities about swollen lymph nodes.
Myth
|
Reality
|
"You should see a doctor immediately whenever you have swollen lymph nodes." | Lymph nodes are constantly filtering lymph, so it is expected that they will change in size with varying amounts of debris or pathogens that may be present. A minor, unnoticed infection may cause swollen lymph nodes that may last for a few weeks. Generally, lymph nodes that return to their normal size within two or three weeks are not a cause for concern. |
"Swollen lymph nodes mean you have a bacterial infection." | Although an infection is the most common cause of swollen lymph nodes, not all infections are caused by bacteria. Mononucleosis, for example, commonly causes swollen lymph nodes, and it is caused by viruses. There are also other causes of swollen lymph nodes besides infections, such as cancer and certain medications. |
"A swollen lymph node means you have cancer." | Cancer is far less likely to be the cause of a swollen lymph node than is an infection. However, if a lymph node remains swollen longer than a few weeks — especially in the absence of an apparent infection — you should have your doctor check it. |
"Cancer in a lymph node always originates somewhere else. There is no cancer of the lymph nodes." | Cancers do commonly spread from their site of origin to nearby lymph nodes and then to other organs, but cancer may also originate in the lymph nodes. This type of cancer is called lymphoma. |
17.3 Summary
- The is a collection of organs involved in the production, maturation, and harboring of called . It also includes a network of vessels that transport or filter the fluid called in which lymphocytes circulate.
- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces — where it leaks out of blood vessels — to the subclavian veins in the upper chest, where it is returned to the . Lymph is similar in composition to blood . Its main cellular components are lymphocytes.
- Lymphatic vessels called are found in villi that line the small intestine. Lacteals absorb fatty acids from the digestion of lipids in the digestive system. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.
- The primary immune function of the lymphatic system is to protect the body against pathogens and cancerous cells. It is responsible for producing mature lymphocytes and circulating them in lymph. Lymphocytes, which include B cells and T cells, are the subset of white blood cells involved in . They may create a lasting memory of and immunity to specific pathogens.
- All lymphocytes are produced in and then go through a process of maturation in which they “learn” to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the . Both the bone marrow and thymus are considered .
- include the , , and . There are four pairs of tonsils that encircle the throat. The spleen filters blood, as well as lymph. There are hundreds of lymph nodes located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.
17.3 Review Questions
- What is the lymphatic system?
- Summarize the immune function of the lymphatic system.
- Explain the difference between lymphocyte maturation and lymphocyte activation.
17.3 Explore More
https://youtu.be/RMLPwOiYnII
What is Lymphoedema or Lymphedema? Compton Care, 2016.
https://youtu.be/ah74jT00jBA
Spleen physiology What does the spleen do in 2 minutes, Simple Nursing, 2015.
https://youtu.be/L4KexZZAdyA
How to check your lymph nodes, University Hospitals Bristol and Weston NHS FT, 2020.
Attributions
Figure 17.3.1
512px-Tonsillitis by Michaelbladon at English Wikipedia on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Transferred from en.wikipedia to Commons by Kauczuk)
Figure 17.3.2
Blausen_0623_LymphaticSystem_Female by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 17.3.3
2201_Anatomy_of_the_Lymphatic_System (cropped) by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 17.3.4
1000px-Intestinal_villus_simplified.svg by Snow93 on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 17.3.5
2206_The_Location_Structure_and_Histology_of_the_Thymus by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 17.3.6
Blausen_0861_Tonsils&Throat_Anatomy2 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 17.3.7
Figure_42_02_14 by CNX OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.
Figure 17.3.8
Illu_lymph_node_structure by NCI/ SEER Training on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Archives: https://web.archive.org/web/20070311015818/http://training.seer.cancer.gov/module_anatomy/unit8_2_lymph_compo1_nodes.html)
Figure 17.3.9
1000px-Lymph_node_regions.svg by Fred the Oyster (derivative work) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original by NCI/ SEER Training)
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 21.2 Anatomy of the lymphatic system [digital image]. In Anatomy and Physiology (Section 21.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/21-1-anatomy-of-the-lymphatic-and-immune-systems
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 21.7 Location, structure, and histology of the thymus [digital image]. In Anatomy and Physiology (Section 21.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/21-1-anatomy-of-the-lymphatic-and-immune-systems
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436
Compton Care. (2016, March 7). What is lymphoedema or lymphedema? YouTube. https://www.youtube.com/watch?v=RMLPwOiYnII&feature=youtu.be
OpenStax. (2016, May 27) Figure 14. The spleen is similar to a lymph node but is much larger and filters blood instead of lymph [digital image]. In Open Stax, Biology (Section 42.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.8:etZobsU-@6/Adaptive-Immune-Response
Simple Nursing. (2015, June 28). Spleen physiology What does the spleen do in 2 minutes. YouTube. https://www.youtube.com/watch?v=ah74jT00jBA&feature=youtu.be
University Hospitals Bristol and Weston NHS FT. (2020, May 13). How to check your lymph nodes. YouTube. https://www.youtube.com/watch?v=L4KexZZAdyA&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
The Kiss of Death
The photomicrograph in Figure 17.5.1 shows a group of killer T cells (green and red) surrounding a cell (blue, centre). When a killer T cell makes contact with the cancer cell, it attaches to and spreads over the dangerous target. The killer T cell then uses special chemicals stored in (red) to deliver the killing blow. This event has thus been nicknamed “the kiss of death.” After the target cell is killed, the killer T cells move on to find the next victim. Killer T cells like these are important players in the adaptive immune system.
What Is the Adaptive Immune System?
The is a subsystem of the overall immune systemno post. It is composed of highly specialized cells and processes that eliminate specific and tumor cells. An adaptive immune response is set in motion by s that the immune system recognizes as foreign. Unlike an innate immune response, an adaptive immune response is highly specific to a particular pathogen (or its antigen). An important function of the adaptive immune system that is not shared by the innate immune system is the creation of immunological memory — or — which occurs after the initial response to a specific pathogen. It allows for a faster, stronger response on subsequent encounters with the same pathogen, usually before the pathogen can even cause symptoms of illness.
are the main cells of the adaptive immune system. They are s that arise and mature in organs of the lymphatic system, including the and . The human body normally has about 2 trillion lymphocytes, which constitute about 1/3 of all leukocytes. Most of the lymphocytes are normally sequestered within tissue fluid or organs of the lymphatic system, including the s, , and s. Only about 2% of the lymphocytes are normally circulating in the blood. There are two main types of lymphocytes involved in adaptive immune responses, called T cells and B cells. T cells destroy infected cells or release chemicals that regulate immune responses. B cells secrete that bind with s[/pb_glossary] of [pb_glossary id="271"]pathogens so they can be removed by other immune cells or processes.
Pathways of the Adaptive Immune Response
There are some general similarities in the way in which the separate adaptive immune responses occur in T cell and B cell responses. In both pathways, a foreign antigen is recognized by the B or T cell. From there, cytokines produced by helper T-cells promote clonal expansion of lymphocytes. From this clonal expansion, two types of B or T cells are produced- cells that directly fight the pathogen invasion and cells that remain behind to provide long-term . Finally, once the pathogen invasion has been eradicated, the plasma cells and killer T cells go through apoptosis (programmed cell death).
T Cells
There are multiple types of , or T lymphocytes. Major types are and . Both types develop from immature T cells that become activated by exposure to an .
T Cell Activation (or Cell-Mediated Immunity)
T cells must be activated to become either killer T cells or helper T cells. This requires presentation of a foreign antigen by , as shown in Figure 17.5.2. Antigen-presenting cells may be , s, or s. Activation occurs when T cells are presented with a foreign antigen coupled with an MHC self antigen. Helper T cells are more easily activated than killer T cells. Activation of killer T cells is strongly regulated and may require additional stimulation from helper T cells.
Killer T Cells
Activated killer T cells induce the death of cells that bear a specific antigen because they are infected with pathogens or are cancerous. The antigen targets the cell for destruction by killer T cells, which travel through the bloodstream searching for target cells to kill. Killer T cells may use various mechanisms to kill target cells. One way is by releasing toxins in granules that enter and kill infected or cancerous cells (see Figure 17.5.3).
Helper T Cells
Activated do not kill infected or cancerous cells. Instead, their role is to “manage” both and responses by directing other cells to perform these tasks. They control other cells by releasing s, which are proteins that can influence the activity of many cell types, including s, , and . Some cytokines released by helper T cells assist with the activation of killer T cells.
B Cells
s, or B lymphocytes, are the major cells involved in the creation of that circulate in blood and . Antibodies are large, Y-shaped proteins used by the immune systemno post to identify and neutralize foreign invaders. Besides producing antibodies, B cells may also function as s, or secrete cytokines that help control other immune cells and responses.
B Cell Activation (or Antibody-Mediated Immunity)
Before B cells can actively function to defend the host, they must be activated. As shown in Figure 17.5.4, B cell activation begins when a B cell engulfs and digests an antigen. The antigen may be either free floating in the lymph, or it may be presented by an antigen-presenting cell, such as a dendritic cell or macrophage. In either case, the B cell then displays antigen fragments bound to its own MHC antigens. The MHC-antigen complex on the B cell attracts helper T cells. The helper T cells, in turn, secrete cytokines that help the B cell to multiply, and the daughter cells to mature into plasma cells.
Plasma Cells
s are antibody-secreting cells that form from activated B cells. Each plasma cell is like a tiny antibody factory. It may secrete millions of copies of an antibody, each of which can bind to the specific antigen that activated the original B cell. The specificity of an antibody to a specific antigen is illustrated in Figure 17.5.5. When antibodies bind with antigens, it makes the cells bearing them easier targets for phagocytes to find and destroy. Antibody-antigen complexes may also trigger the complement system of the innate immune system, which destroys the cells in a cascade of protein enzymes. In addition, the complexes are likely to clump together (agglutinate). If this occurs, they are filtered out of the blood in the spleen or liver.
Immunity
Once a pathogen has been cleared from the body, most activated T cells and B cells die within a few days. A few of the cells, however, survive and remain in the body as memory T cells or memory B cells. These are ready to activate an immediate response if they are exposed to the same antigen again in the future. This is the basis of .
The earliest known reference to the concept of immunity relates to the bubonic plaque (see Figure 17.5.6). In 430 B.C., a Greek historian and general named Thucydides noted that people who had recovered from a previous bout of the plague could nurse people who were sick with the plague without contracting the illness a second time. We now know that this is true of many diseases, and that it occurs because of active immunity.
Active Immunity
is the ability of the adaptive immune system to resist a specific pathogen because it has formed an immunological memory of the pathogen. Active immunity is adaptive, because it occurs during the lifetime of an individual as an adaptation to infection with a specific pathogen, and prepares the immune system for future challenges from that pathogen. Active immunity can come about naturally or artificially.
Naturally Acquired Active Immunity
Active immunity is acquired naturally when a pathogen invades the body and activates the adaptive immune system. When the initial infection is over, memory B cells and memory T cells remain, providing immunological memory of the pathogen. As long as the memory cells are alive, the immune system is ready to mount an immediate response if the same pathogen tries to infect the body again.
Artificially Acquired Active Immunity
Active immunity can also be acquired artificially through immunization. is the deliberate exposure of a person to a pathogen in order to provoke an adaptive immune response and the formation of memory cells specific to that pathogen. The pathogen is introduced in a vaccine — usually by injection, sometimes by nose or mouth (see Figure 17.5.7) — so immunization is also called vaccination.
Typically, only part of a pathogen, a weakened form of the pathogen, or a dead pathogen is used in a vaccine, which causes an adaptive immune response without making the immunized person sick. This is how you most likely became immune to diseases such as measles, mumps, and chicken pox. Immunizations may last for a lifetime, or they may require periodic booster shots to maintain immunity. While immunization generally has long-lasting effects, it usually takes several weeks to develop full immunity.
Immunization is the most effective method ever discovered of preventing infectious diseases. As many as 3 million deaths are prevented each year because of vaccinations. Widespread immunity from vaccinations is largely responsible for the worldwide eradication of smallpox, and the near elimination of several other infectious diseases from many populations, including polio and measles. Immunization is so successful because it exploits the natural specificity and inducibility of the adaptive immune system.
Passive Immunity
results when pathogen-specific antibodies or activated T cells are transferred to a person who has never been exposed to the pathogen. Passive immunity provides immediate protection from a pathogen, but the adaptive immune system does not develop immunological memory to protect the host from the same pathogen in the future. Unlike active immunity, passive immunity lasts only as long as the transferred antibodies or T cells survive in the blood — usually between a few days and a few months. However, like active immunity, passive immunity can be acquired both naturally and artificially.
Naturally Acquired Passive Immunity
Passive immunity is acquired naturally by a fetus through its mother’s blood. are transported from mother to fetus across the placenta, so babies have high levels of antibodies at birth. Their antibodies have the same range of antigen specificities as their mother’s. Passive immunity may also be acquired by an infant through the mother’s breast milk. This gives young infants protection from common pathogens in their environment while their own immune system matures.
Artificially Acquired Passive Immunity
Older children and adults can acquire passive immunity artificially through the injection of antibodies or activated T cells, which may be done when there is a high risk of infection and insufficient time for the body to develop active immunity through vaccination. It may also be done to reduce symptoms of ongoing disease, or to compensate for immunodeficiency diseases.
Adaptive Immune Evasion
Many pathogens have been around for a long time, living with human populations for generations. To persist, some have evolved mechanisms to evade the adaptive immune system of human hosts. One way they have done this is by rapidly changing their non-essential antigens. This is called antigenic variation. An example of a pathogen that takes this approach is human immunodeficiency virus (HIV). It mutates rapidly so the proteins on its viral envelope are constantly changing. By the time the adaptive immune system responds, the virus’s antigens have changed. Antigenic variation is the main reason that efforts to develop a vaccine against HIV have not yet been successful.
Another evasion approach that some pathogens may take is to mask pathogen antigens with host molecules so the host’s immune system cannot detect the antigens. HIV takes this approach, as well. The envelope that covers the virus is formed from the outermost membrane of the host cell.
Feature: My Human Body
If you think that immunizations are just for kids, think again. There are several vaccines recommended by HealthLinkBC for people over the age of 18. The tables below from HealthLinkBC show the vaccine schedules recommended for infants and children, school-aged children, and adults and senior. Additional vaccines may be recommended for certain adults based on specific travel plans, medical conditions or other indications. Are you up to date with your vaccines? You can check with your doctor to be sure.
17.5 Summary
- The is a subsystem of the overall immune system that recognizes and makes a tailored attack against specific or tumor cells. It is a slower, but more effective response than the , and also leads to immunity to particular pathogens.
- produced by the are the main cells of the adaptive immune system. There are two major types of lymphocytes: and . Both types must be activated by foreign to become functioning immune cells.
- Most activated T cells become either or . Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing that control other types of leukocytes.
- Activated B cells form that secrete , which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the .
- After an adaptive immune response occurs, long-lasting may remain to confer immunity to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.
- Immunity may be active or passive. Active immunity occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.
- Passive immunity occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus () evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host’s cell membrane.
17.5 Review Questions
- What is the adaptive immune system?
- Define immunity.
- How are lymphocytes activated?
- Identify two common types of T cells and their functions.
- How do activated B cells help defend against pathogens?
- How does passive immunity differ from active immunity? How may passive immunity occur?
- What are two ways that active immunity may come about?
- What ways of evading the human adaptive immune system evolved in human immunodeficiency virus (HIV)?
- Why do vaccinations expose a person to a version of a pathogen?
17.5 Explore More
https://youtu.be/rb7TVW77ZCs
How do vaccines work? - Kelwalin Dhanasarnsombut, TED-Ed, 2015.
https://youtu.be/yqUFy-t4MlQ
How we conquered the deadly smallpox virus - Simona Zompi, TED-Ed, 2013.
https://youtu.be/5THf6gTNqO8
Why Do We Need A New Flu Shot Every Year? Seeker, 2015.
https://youtu.be/X-rC78MKZvw
An HIV Vaccine: Mapping Uncharted Territory, NIAID, 2016.
Attributions
Figure 17.5.1
Killer_T_cells_surround_a_cancer_cell by Alex Ritter, Jennifer Lippincott Schwartz and Gillian Griffiths at the National Institutes of Health/ Visuals Online on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 17.5.2
T_cell_activation.svg by Rehua (derivative work) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original image: T_cell_activation.png: from The Immune System - NIH Publication No. 03–5423)
Figure 17.5.3
Cytotoxic T Cell function by CNX OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.
Figure 17.5.4
B_cell_activation.svg by Fred the Oyster on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original from The Immune System - NIH Publication No. 03–5423)
Figure 17.5.5
Antibody.svg by Fvasconcellos on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original black and white image from the National Human Genome Research Institute's Talking Genetics Glossary)
Figure 17.5.7
immunizations by U.S. Air Force photo by Airman 1st Class Destinee Dougherty from Military Health System website, Health.mil, is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
HealthLinkBC. (2018). B.C. immunization schedules. Gov.BC.CA. https://www.healthlinkbc.ca/tools-videos/bc-immunization-schedules
Mayo Clinic Staff. (n.d.). Measles [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/measles/symptoms-causes/syc-20374857
Mayo Clinic Staff. (n.d.). Mumps [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/mumps/symptoms-causes/syc-20375361
Mayo Clinic Staff. (n.d.). Polio [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/polio/symptoms-causes/syc-20376512
Mayo Clinic Staff. (n.d.). Smallpox [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/smallpox/symptoms-causes/syc-20353027
NIAID. (2016, August 11). An HIV vaccine: Mapping uncharted territory. YouTube. https://www.youtube.com/watch?v=X-rC78MKZvw&feature=youtu.be
OpenStax. (2016, March 23). Figure 4 Naïve
Seeker. (2015, September 2). Why do we need a new flu shot every year? YouTube. https://www.youtube.com/watch?v=5THf6gTNqO8
TED-Ed. (2015, January 12). How do vaccines work? - Kelwalin Dhanasarnsombut. YouTube. https://www.youtube.com/watch?v=rb7TVW77ZCs&feature=youtu.be
TED-Ed. (2013, October 28). How we conquered the deadly smallpox virus - Simona Zompi. YouTube. https://www.youtube.com/watch?v=yqUFy-t4MlQ&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Case Study Conclusion: Defending Your Defenses
These people are participating in a bike ride to raise funds for leukemia and lymphoma research (Figure 17.7.1). Leukemia and lymphoma are blood cancers. In 2020, approximately 6,900 Canadians will be diagnosed with leukemia and 3,000 will die from this cancer. Lymphoma is the most common type of blood cancer. As a lymphoma patient, Hakeem, who you learned about in the beginning of this chapter, may eventually benefit from research funded by a bike ride like this one.
What type of blood cell is affected in ? As the name implies, lymphoma is a cancer that affects lymphocytes, which are a type of leukocyte. As you have learned in this chapter, there are different types of lymphocytes, including the B and T cells of the . Different types of lymphoma affect different types of lymphocytes in different ways. It is important to correctly identify the type of lymphoma, so that patients can be treated appropriately.
You may recall that one of Hakeem’s symptoms was a swollen , and he was diagnosed with lymphoma after a biopsy of that lymph node. Swollen lymph nodes are a common symptom of lymphoma. As you have learned, lymph nodes are distributed throughout the body along lymphatic vessels, as part of the . The lymph nodes filter and store lymphocytes. Therefore, they play an important role in fighting infections. Because of this, they will often swell in response to an infection. In Hakeem’s case, the swelling and other symptoms did not improve after several weeks and a course of antibiotics, which caused Dr. Hayes to suspect lymphoma instead. The biopsy showed that Hakeem did indeed have cancerous lymphocytes in his lymph nodes.
But which type of lymphocytes were affected? Lymphoma most commonly affects B or T lymphocytes. The two major types of lymphoma are called Hodgkin (HL) or non-Hodgkin lymphoma (NHL). NHL is more common than HL. In 2020, the Canadian Cancer Society estimates 10,400 Canadians will be diagnosed with non-Hodgkin lymphoma, whereas 1,000 will be diagnosed with Hodgkin lymphoma. While HL is one distinct type of lymphoma, NHL has about 60 different subtypes, depending on which specific cells are affected and how.
Hakeem was diagnosed with a type of NHL called diffuse large B-cell lymphoma (DLBCL) — the most common type of NHL. This type of lymphoma affects and causes them to appear large under the microscope. In addition to Hakeem’s symptoms of fatigue, swollen lymph nodes, loss of appetite, and weight loss, common symptoms of this type of lymphoma include fever and night sweats. It is an aggressive and fast-growing type of lymphoma that is fatal if not treated. The good news is that with early detection and proper treatment, about 70% of patients with DLBCL can be cured.
How do physicians determine the specific type of lymphoma? Tissue obtained from a biopsy can be examined under a microscope to observe physical changes (such as abnormal cell size or shape) that are characteristic of a particular subtype of lymphoma. Additionally, tests can be performed on the tissue to determine which cell-surface antigens are present. Recall that antigens are molecules that bind to specific antibodies. can be produced in the laboratory and labeled with compounds that can be identified by their colour under a microscope. When these antibodies are applied to a tissue sample, this colour will appear wherever the antigen is present, because it binds to the antibody. This technique was used in the photomicrograph in Figure 17.7.2 to identify the presence of a cell-surface antigen (shown as reddish-brown) in a sample of skin cells. This technique, called immunohistochemistry, is also commonly used to identify antigens in tissue samples from lymphoma patients.
Why would identifying cell-surface antigens be important in diagnosing and treating lymphoma? As you have learned, the immune system uses antigens present on the surface of cells or pathogens to distinguish between self and non-self, and to launch adaptive immune responses. Cells that become cancerous often change their cell-surface antigens. This is one way that the immune system can identify and destroy them. Also, different cell types in the body can sometimes be identified by the presence of specific cell-surface antigens. Knowing the types of cell-surface antigens present in a tissue sample can help physicians identify which cells are cancerous, and possibly the specific subtype of cancer. Knowing this information can be helpful in choosing more tailored and effective treatments.
One treatment for NHL is, in fact, the use of medications made from antibodies that bind to cell-surface antigens present on cells affected by the specific subtype of NHL. This is called . These drugs can directly bind to and kill the cancerous cells. For patients with DLBCL like Hakeem, immunotherapy is often used in conjunction with and radiation as a course of treatment. Although Hakeem has a difficult road ahead, he and his medical team are optimistic that — given the high success rate when DLBCL is caught and treated early — he may be cured. More research into how the immune system functions may lead to even better treatments for lymphoma — and other types of cancers — in the future.
Chapter 17 Summary
In this chapter, you learned about the immune system. Specifically, you learned that:
- Any agent that can cause disease is called a . Most human pathogens are , such as and . The immune system is the body system that defends the human host from pathogens and cells.
- The is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.
- The is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to to the pathogens.
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.
- are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells () respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.
- An important role of the immune system is tumor surveillance. of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.
- The that protects the is thought to be distinct from the that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out .
- The is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called . The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.
-
- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the . Lymph is similar in composition to blood . Its main cellular components are lymphocytes.
- Lymphatic vessels called are found in that line the . Lacteals absorb fatty acids from the digestion of lipids in the . The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.
- Lymphocytes, which include and , are the subset of leukocytes involved in . They may create a lasting memory of and to specific pathogens.
- All lymphocytes are produced in and then go through a process of maturation, in which they “learn” to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the . Both the bone marrow and thymus are considered .
- include the tonsils, spleen, and lymph nodes. There are four pairs of that encircle the throat. The filters blood, as well as lymph. There are hundreds of located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.
- Unlike the adaptive immune system, the does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.
-
- The body’s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.
-
-
- — which include the , , and fluids (such as tears and ) — physically block pathogens from entering the body.
- Chemical barriers — such as enzymes in , , and — kill pathogens on body surfaces.
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.
- If pathogens breach the protective barriers, occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as and ), and it causes swelling, redness, and warmth.
- The is a complex biochemical mechanism that helps kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the of pathogens and bursting of the cells.
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, , , and phagocytize pathogens. and release chemicals that trigger inflammation. destroy cancerous or virus-infected cells, and kill parasites.
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.
-
- The main cells of the adaptive immune system are . There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.
-
- Most activated T cells become either or . Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.
- Activated B cells form s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.
- After an adaptive immune response occurs, long-lasting may remain to confer to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.
- Immunity may be active or passive.
-
- occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.
- occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus () evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host’s cell membrane.
- An is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen that causes allergies is called an . Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).
-
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system “keeps busy” by attacking harmless antigens.
- Allergies occur when B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.
- Mild allergy symptoms are frequently treated with antihistamines that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called , is a medical emergency that is usually treated with injections of epinephrine. for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.
- occur when the immune system fails to recognize the body’s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.
-
- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.
- Immunodeficiency occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.
-
- is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. occurs because of some event or exposure experienced after birth. Possible causes include substance abuse, obesity, and malnutrition, among others.
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with (AIDS). Medications can control the multiplication of HIV in the human body, but it can't eliminate the virus completely.
Up to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals — the reproductive system.
Chapter 17 Review
- Compare and contrast a pathogen and an allergen.
- Describe three ways in which pathogens can enter the body.
- The complement system involves the activation of several proteins to kill pathogens. Why do you think this is considered part of the innate immune system, instead of the adaptive immune system?
- Why are innate immune responses generally faster than adaptive immune responses?
- Explain how an autoimmune disease could be triggered by a pathogen.
- What is an opportunistic infection? Name two diseases or conditions that could result in opportunistic infections. Explain your answer.
- Which cell type in the immune system can be considered an “antibody factory?"
- Besides foreign pathogens, what is one thing that the immune system protects the body against?
- What cell type in the immune system is infected and killed by HIV?
- Name two types of cells that produce cytokines in the immune system. What are two functions of cytokines in the immune system?
- Many pathogens evade the immune system by altering their outer surface in some way. Based on what you know about the functioning of the immune system, why is this often a successful approach?
- What is “missing self?" How does this condition arise?
17.7 Explore More
https://youtu.be/Z3B-AaqjyjE
What is leukemia? - Danilo Allegra and Dania Puggioni, TED-Ed, 2015.
Attributions
Figure 17.7.1
Cycling to Beat Blood Cancer by Blood Cancer UK (Formerly Bloodwise) on Flickr is used under a CC BY-NC-ND 2.0 (https://creativecommons.org/licenses/by-nc-nd/2.0/) license.
Figure 17.7.2
antigen stain by Ed Uthman from Houston, TX, USA on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
References
Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https://www.cancer.ca:443/en/cancer-information/cancer-type/hodgkin-lymphoma/statistics/?region=on
Non-Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https://www.cancer.ca:443/en/cancer-information/cancer-type/non-hodgkin-lymphoma/statistics/?region=on
TED-Ed. (2015, April 30). What is leukemia? - Danilo Allegra and Dania Puggioni. YouTube. https://www.youtube.com/watch?v=Z3B-AaqjyjE&feature=youtu.be
A glucocorticoid hormone produced by the cortex of the adrenal gland that is released in response to stress and also helps control metabolic rate, suppression of the immune system, and other functions
Created by CK-12 Foundation/Adapted by Christine Miller
It’s All about Sex
A tiny from dad breaks through the surface of a huge egg from mom. Voilà! In nine months, a new son or daughter will be born. Like most other multicellular organisms, human beings reproduce sexually. In human sexual reproduction, males produce sperm and females produce eggs, and a new offspring forms when a sperm unites with an egg. How do sperm and eggs form? And how do they arrive together at the right place and time so they can unite to form a new offspring? These are functions of the reproductive system.
What Is the Reproductive System?
The is the human organ system responsible for the production and fertilization of gametes (sperm or eggs) and, in females, the carrying of a fetus. Both male and female reproductive systems have organs called s that produce gametes. A is a cell that combines with another haploid gamete during , forming a single diploid cell called a . Besides producing gametes, the gonads also produce sex hormones. are endocrine hormones that control the development of sex organs before birth, sexual maturation at puberty, and reproduction once sexual maturation has occurred. Other reproductive system organs have various functions, such as maturing gametes, delivering gametes to the site of fertilization, and providing an environment for the development and growth of an offspring.
Sex Differences in the Reproductive System
The reproductive system is the only human organ system that is significantly different between males and females. Embryonic structures that will develop into the reproductive system start out the same in males and females, but by birth, the reproductive systems have differentiated. How does this happen?
Sex Differentiation
Starting around the seventh week after conception in genetically male (XY) embryos, a gene called SRY on the Y chromosome (shown in Figure 18.2.2) initiates the production of multiple proteins. These proteins cause undifferentiated gonadal tissue to develop into male gonads (testes). The male gonads then secrete hormones — including the male sex hormone testosterone — that trigger other changes in the developing offspring (now called a fetus), causing it to develop a complete male reproductive system. Without a Y chromosome, an embryo will develop female gonads (ovaries) that will produce the female sex hormone estrogen. Estrogen, in turn, will lead to the formation of the other organs of a normal female reproductive system.
Homologous Structures
Undifferentiated embryonic tissues develop into different structures in male and female . Structures that arise from the same tissues in males and females are called s. The male testes and female ovaries, for example, are homologous structures that develop from the undifferentiated gonads of the embryo. Likewise, the male penis and female clitoris are homologous structures that develop from the same embryonic tissues.
Sex Hormones and Maturation
Male and female reproductive systems are different at birth, but they are immature and incapable of producing gametes or sex hormones. Maturation of the reproductive system occurs during puberty, when hormones from the and stimulate the testes or ovaries to start producing sex hormones again. The main sex hormones are in males and in females. Sex hormones, in turn, lead to the growth and maturation of the reproductive organs, rapid body growth, and the development of secondary sex characteristics. s are traits that are different in mature males and females, but are not directly involved in reproduction. They include facial hair in males and breasts in females.
Male Reproductive System
The main structures of the male reproductive system are external to the body and illustrated in Figure 18.2.3. The two (singular, testis) hang between the thighs in a sac of skin called the . The testes produce both and . Resting atop each testis is a coiled structure called the (plural, epididymes). The function of the epididymes is to mature and store sperm. The is a tubular organ that contains the urethra and has the ability to stiffen during sexual arousal. Sperm passes out of the body through the urethra during a sexual climax (orgasm). This release of sperm is called ejaculation.
In addition to these organs, the male reproductive system consists of several ducts and glands that are internal to the body. The ducts, which include the (also called the ductus deferens), transport sperm from the to the . The glands, which include the and , produce fluids that become part of semen. is the fluid that carries sperm through the urethra and out of the body. It contains substances that control pH and provide sperm with nutrients for energy.
Female Reproductive System
The main structures of the female reproductive system are internal to the body and shown in the following figure. They include the paired , which are small, ovoid structures that produce and secrete . The two (sometimes called Fallopian tubes or uterine tubes) start near the ovaries and end at the . Their function is to transport ova from the ovaries to the uterus. If an egg is fertilized, it usually occurs while it is traveling through an oviduct. The uterus is a pear-shaped muscular organ that functions to carry a fetus until birth. It can expand greatly to accommodate a growing fetus, and its muscular walls can contract forcefully during labour to push the baby out of the uterus and into the vagina. The is a tubular tract connecting the uterus to the outside of the body. The vagina is where sperm are usually deposited during and . The vagina is also called the birth canal because a baby travels through the vagina to leave the body during birth.
The external structures of the female reproductive system are referred to collectively as the . They include the , which is homologous to the male penis. They also include two pairs of (singular, labium), which surround and protect the openings of the urethra and vagina.
18.2 Summary
- The is the human organ system responsible for the production and of and, in females, the carrying of a .
- Both male and female reproductive systems have organs called ( in males, in females) that produce gametes ( or ova) and sex hormones (such as in males and in females). Sex are endocrine hormones that control the prenatal development of reproductive organs, sexual maturation at puberty, and reproduction after .
- The reproductive system is the only organ system that is significantly different between males and females. A Y-chromosome gene called SRY is responsible for undifferentiated embryonic tissues developing into a male reproductive system. Without a Y chromosome, the undifferentiated embryonic tissues develop into a female reproductive system.
- Structures such as testes and ovaries that arise from the same undifferentiated embryonic tissues in males and females are called .
- Male and female reproductive systems are different at birth, but at that point, they are immature and nonfunctioning. Maturation of the reproductive system occurs during puberty, when hormones from the and stimulate the gonads to produce sex hormones again. The sex hormones, in turn, cause the changes of puberty.
- Male reproductive system organs include the , , , , , and .
- Female reproductive system organs include the , , , , , and .
18.2 Review Questions
- What is the reproductive system?
- Explain the difference between the vulva and the vagina.
18.2 Explore More
https://youtu.be/kMWxuF9YW38
Sex Determination: More Complicated Than You Thought, TED-Ed, 2012.
https://youtu.be/vcPJkz-D5II
The evolution of animal genitalia - Menno Schilthuizen, TED-Ed, 2017.
https://youtu.be/l5knvmy1Z3s
Hormones and Gender Transition, Reactions, 2015.
Attributions
Figure 18.2.1
Sperm-egg by Unknown author on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain).
Figure 18.2.2
Y Chromosome by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.2.3
3D_Medical_Animation_Vas_Deferens by https://www.scientificanimations.com on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.2.4
Blausen_0399_FemaleReproSystem_01 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
Reactions. (2015, June 8). Hormones and gender transition. YouTube. https://www.youtube.com/watch?v=l5knvmy1Z3s&feature=youtu.be
TED-Ed. (2012, April 23). Sex determination: More complicated than you thought. YouTube. https://www.youtube.com/watch?v=kMWxuF9YW38&feature=youtu.be
TED-Ed. (2017, April 24). The evolution of animal genitalia - Menno Schilthuizen. YouTube. https://www.youtube.com/watch?v=vcPJkz-D5II&feature=youtu.be
A type of disease in which cells of the central nervous system stop working or die. Neurodegenerative disorders usually get worse over time and have no cure. They may be genetic or be caused by a tumor or stroke.
Created by CK-12 Foundation/Adapted by Christine Miller
Colourful Sperm
This false-colour image (Figure 18.4.1) shows real human sperm. The tiny gametes are obviously greatly magnified in the picture, because they are actually the smallest of all human cells. In fact, human sperm cells are small, even when compared with sperm cells of other animals. Mice sperm are about twice the length of human sperm! Human sperm may be small in size, but in a normal, healthy man, huge numbers of them are usually released during each ejaculation. There may be hundreds of millions of sperm cells in a single teaspoon of semen. Producing sperm is one of the major functions of the male reproductive system.
Sperm Anatomy
A mature sperm cell has several structures that help it reach and penetrate an egg. These are labeled in the drawing of a sperm shown in Figure 18.4.2.
- The is the part of the sperm that contains the nucleus — and not much else. The nucleus, in turn, contains tightly coiled DNA that is the male parent’s contribution to the genetic makeup of a zygote (if one forms). Each sperm is a haploid cell, containing half the chromosomal complement of a normal, diploid body cell.
- The front of the head is an area called the . The acrosome contains enzymes that help the sperm penetrate an ovum (if it reaches one).
- The is the part of the sperm between the head and the flagellum. The midpiece is packed with mitochondria that produce the energy needed to move the flagellum.
- The (also called the tail) can rotate like a propeller, allowing the sperm to “swim” through the female reproductive tract to reach an ovum if one is present.
Spermatogenesis
The process of producing sperm is known as . Spermatogenesis normally starts when a male reaches , and it usually continues uninterrupted until death, although a decrease in sperm production generally occurs at older ages. A young, healthy male may produce hundreds of millions of sperm a day! Only about half of these, however, are likely to become viable, mature sperm.
Where Sperm Are Produced
Spermatogenesis occurs in the in the testes. Spermatogenesis requires high concentrations of testosterone. is secreted by , which are adjacent to the seminiferous tubules in the testes.
Sperm production in the seminiferous tubules is very sensitive to temperature. This may be the most important reason the testes are located outside the body in the scrotum. The temperature inside the scrotum is generally about 2 degrees Celsius cooler than core body temperature. This lower temperature is optimal for spermatogenesis. The scrotum regulates its internal temperature as needed by contractions of the smooth muscles lining the scrotum. When the temperature inside the scrotum becomes too low, the scrotal muscles contract. The contraction of the muscles pulls the scrotum higher against the body, where the temperature is warmer. The opposite occurs when the temperature inside the scrotum becomes too high.
Events of Spermatogenesis
Figure 18.4.3 summarizes the main cellular events that occur in the process of spermatogenesis. The process begins with a diploid stem cell called a (plural, spermatogonia), and involves several cell divisions. The entire process takes at least ten weeks to complete, including maturation in the .
- A spermatogonium undergoes to produce two cells called primary spermatocytes. One of the primary spermatocytes goes on to produce . The other replenishes the reserve of spermatogonia.
- The primary spermatocyte undergoes meiosis I to produce two haploid daughter cells called secondary spermatocytes.
- The secondary spermatocytes rapidly undergo meiosis II to produce a total of four daughter cells called spermatids.
- The spermatids begin to form a tail, and their becomes highly condensed. Unnecessary cytoplasm and organelles are removed from the cells, and they form a head, midpiece, and flagellum. The resulting cells are sperm (spermatozoa).
As shown in Figure 18.4.4, the events of begin near the wall of the seminiferous tubule — where spermatogonia are located — and continue inward toward the lumen of the tubule. extend from the wall of the seminiferous tubule inward toward the lumen, so they are in contact with developing sperm at all stages of spermatogenesis. Sertoli cells play several roles in spermatogenesis:
- They secrete endocrine that help regulate spermatogenesis.
- They secrete substances that initiate .
- They concentrate testosterone (from ), which is needed at high levels to maintain spermatogenesis.
- They the extra cytoplasm that is shed from developing sperm cells.
- They secrete testicular fluid that helps carry sperm into the .
- They maintain a blood-testis barrier, so immune system cells cannot reach and attack the sperm.
Maturation in the Epididymis
Although the sperm produced in the testes have tails, they are not yet motile (able to “swim”). The non-motile sperm are transported to the in testicular fluid that is secreted by with the help of . In the epididymis, the sperm gain motility, so they are capable of swimming up the female genital tract and reaching an ovum. The mature sperm are stored in the epididymis until ejaculation occurs.
Ejaculation
Sperm are released from the body during , which typically occurs during orgasm. Hundreds of millions of mature sperm — contained within a small amount of thick, whitish fluid called — are propelled from the penis during a normal ejaculation.
How Ejaculation Occurs
Ejaculation occurs when of the muscle layers of the and other accessory structures propel sperm from the epididymes, where mature sperm are stored. The muscle contractions force the sperm through the vas deferens and the ejaculatory ducts, and then out of the penis through the urethra. Due to the peristaltic action of the muscles, the ejaculation occurs in a series of spurts.
The Role of Semen
As sperm travel through the ejaculatory ducts during ejaculation, they mix with secretions from the seminal vesicles, prostate gland, and bulbourethral glands to form semen (see Figure 18.4.5 ). The average amount of semen per ejaculate is about 3.7 mL, which is a little less than a teaspoonful. Most of this volume of semen consists of glandular secretions, with the hundreds of millions of sperm cells actually contributing relatively little to the total volume.
The secretions in semen are important for the survival and motility of sperm. They provide a medium through which sperm can swim. They also include sperm-sustaining substances, such as high concentrations of the sugar fructose, which is the main source of energy for sperm. In addition, semen contains many alkaline substances that help neutralize the acidic environment in the female vagina. This protects the DNA in sperm from being denatured by acid, and prolongs the life of sperm in the female reproductive tract.
Erection
Besides providing a way for sperm to leave the body, the main role of the penis in reproduction is , or depositing sperm in the vagina of the female reproductive tract. Intromission depends on the ability of the penis to become stiff and erect, a state referred to as an . The human penis, unlike that of most other mammals, contains no erectile bone. Instead, in order to reach its erect state, it relies entirely on engorgement with blood of its columns of spongy tissue. During sexual arousal, the arteries that supply blood to the dilate, allowing more blood to fill the spongy tissue. The now-engorged spongy tissue presses against and constricts the veins that carry blood away from the penis. As a result, more blood enters than leaves the penis, until a constant erectile size is achieved.
In addition to sperm, the penis also transports urine out of the body. These two functions cannot occur simultaneously. During an erection, the sphincters that prevent urine from leaving the bladder are controlled by centres in the brain so they cannot relax and allow urine to enter the urethra.
Testosterone Production
The final major function of the male reproductive system is the production of the male sex hormone . In mature males, this occurs mainly in the testes. Testosterone production is under the control of (LH) from the . LH stimulates in the to secrete testosterone.
Testosterone is important for male sexual development at . It stimulates maturation of the male reproductive organs, as well as the development of secondary male sex characteristics (such as facial hair). Testosterone is also needed in mature males for normal to be maintained in the testes. (FSH) from the pituitary gland is also needed for spermatogenesis to occur, in part because it helps in the testes concentrate testosterone to high enough levels to maintain sperm production. Testosterone is also needed for proper functioning of the . In addition, testosterone plays a role in , allowing sperm to be deposited within the female reproductive tract.
Feature: My Human Body
If you’re a man and you use a laptop computer on your lap for long periods of time, you may be decreasing your fertility. The reason? A laptop computer generates considerable heat, and its proximity to the scrotum during typical use results in a significant rise in temperature inside the scrotum. is very sensitive to high temperatures, so it may be adversely affected by laptop computer use. If you want to avoid the potentially fertility-depressing effect of laptop computer use, you might want to consider using your laptop computer on a table or other surface rather than on your lap — at least when you log on for long computer sessions. Other activities that raise scrotal temperature and have the potential to reduce spermatogenesis including soaking in hot tubs, wearing tight clothing, and biking. Although the effects of short-term scrotal heating on fertility seem to be temporary, years of such heat exposure may cause irreversible effects on sperm production.
18.4 Summary
- Parts of a mature sperm include the , , , and . The process of producing sperm is called spermatogenesis. This normally starts during , and continues uninterrupted until death.
- occurs in the in the , and requires high concentrations of . in the testes play many roles in spermatogenesis, including concentrating testosterone under the influence of from the .
- Spermatogenesis begins with a stem cell called a , which undergoes mitosis to produce a primary spermatocyte. The primary spermatocyte undergoes meiosis I to produce secondary spermatocytes, and these cells in turn undergo meiosis II to produce spermatids. After the spermatids grow a tail and undergo other changes, they become .
- Before sperm are able to “swim,” they must mature in the . The mature sperm are then stored in the epididymis until occurs.
- Ejaculation is the process in which is propelled by in the and from the in the penis. Semen is a whitish fluid that contains sperm and secretions from the , , and . These alkaline secretions are important for sperm survival and motility.
- Besides ejaculating sperm, another reproductive role of the penis is , which is depositing sperm in the female . This requires the penis to become stiff and erect, a state referred to as an . Erection usually occurs with sexual arousal as the columns of spongy tissue inside the penis become engorged with blood.
- in the testes secrete testosterone under the control of (LH) from the pituitary gland. Testosterone is needed for male sexual development at puberty, and to maintain normal spermatogenesis after puberty. It also plays a role in prostate function and penis's ability to become erect.
18.4 Review Questions
- Compare and contrast the terms: erection, ejaculation, and intromission.
- Describe semen and its components.
- Explain how erection occurs.
18.4 Explore More
https://youtu.be/gNHSTa0Yct4
How You're Destroying Your Sperm! Seeker, 2014.
https://youtu.be/krSMZDsjLuU
Human Physiology - Reproduction: Spermatogenesis, Janux, 2015.
Attributions
Figure 18.4.1
Sperm-20051108 by Gilberto Santa Rosa from Rio de Janeiro, Brazil on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 18.4.2
Sperm Anatomy by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.4.3
Spermatogenesis by OpenStax College is used and adapted by Christine Miller under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.4.4
Testis-cross-section by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
Figure 18.4.5
Human_semen_in_a_petri_dish by Digitalkil on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:public_domain).
Figure 18.4.6
Laptop by logan-weaver-b76PEyeIptQ-unsplash [photo] by LOGAN WEAVER on Unsplash is used under the Unsplash License (https://unsplash.com/license).
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 27.5 Spermatogenesis [digital image]. In Anatomy and Physiology (Section 27.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/27-1-anatomy-and-physiology-of-the-male-reproductive-system
Brainard, J/ CK-12 Foundation. (2016). Figure 4 Cross-section of a testis and seminiferous tubules [digital image]. In CK-12 College Human Biology (Section 20.4) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/20.4/
Janux. (2015, January 10). Human physiology - Reproduction: spermatogenesis. YouTube. https://www.youtube.com/watch?v=krSMZDsjLuU&feature=youtu.be
Seeker. (2014, June 16). How you're destroying your sperm! YouTube. https://www.youtube.com/watch?v=gNHSTa0Yct4&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Taboo Topic
The banner in Figure 18.8.1 was carried in a 2014 march in Uganda as part of the celebration of Menstrual Hygiene Day. Menstrual Hygiene Day is an awareness day on May 28 of each year that aims to raise awareness worldwide about menstruation and menstrual hygiene. Maintaining good menstrual hygiene is difficult in developing countries like Uganda because of taboos on discussing menstruation and lack of availability of menstrual hygiene products. Poor menstrual hygiene, in turn, can lead to embarrassment, degradation, and reproductive health problems in females. May 28 was chosen as Menstrual Hygiene Day because of its symbolism. May is the fifth month of the year, and most women average five days of menstrual bleeding each month. The 28th day was chosen because the menstrual cycle averages about 28 days.
What Is the Menstrual Cycle?
The refers to natural changes that occur in the female reproductive system each month during the reproductive years. The cycle is necessary for the production of ova and the preparation of the for . It involves changes in both the ovaries and the uterus, and is controlled by pituitary and ovarian hormones. Day 1 of the cycle is the first day of the menstrual period, when bleeding from the uterus begins as the built-up lining the uterus is shed. The endometrium builds up again during the remainder of the cycle, only to be shed again during the beginning of the next cycle if does not occur. In the ovaries, the menstrual cycle includes the development of a , ovulation of a secondary oocyte, and then degeneration of the follicle if pregnancy does not occur. Both uterine and ovarian changes during the menstrual cycle are generally divided into three phases, although the phases are not the same in the two organs.
Menarche and Menopause
The female reproductive years are delineated by the start and stop of the menstrual cycle. The first menstrual period usually occurs around 12 or 13 years of age, an event that is known as . There is considerable variation among individuals in the age at menarche. It may occasionally occur as early as eight years of age or as late as 16 years of age and still be considered normal. The average age is generally later in the developing world, and earlier in the developed world. This variation is thought to be largely attributable to nutritional differences.
The cessation of menstrual cycles at the end of a woman’s reproductive years is termed . The average age of menopause is 52 years, but it may occur normally at any age between about 45 and 55 years of age. The age of menopause varies due to a variety of biological and environmental factors. It may occur earlier as a result of certain illnesses or medical treatments.
Variation in the Menstrual Cycle
The length of the menstrual cycle — as well as its phases — may vary considerably, not only among different women, but also from month to month for a given woman. The average length of time between the first day of one menstrual period and the first day of the next menstrual period is 28 days, but it may range from 21 days to 45 days. Cycles are considered regular when a woman’s longest and shortest cycles differ by less than eight days. The menstrual period itself is usually about five days long, but it may vary in length from about two days to seven days.
Ovarian Cycle
The events of the menstrual cycle that take place in the ovaries make up the . It consists of changes that occur in the of one of the . The ovarian cycle is divided into the following three phases: follicular phase, ovulation, and luteal phase. These phases are illustrated in Figure 18.8.2.
Follicular Phase
The is the first phase of the ovarian cycle. It generally lasts about 12 to 14 days for a 28-day menstrual cycle. During this phase, several are stimulated to begin maturing, but usually only one — called the Graafian follicle — matures completely so it is ready to release an egg. The other maturing follicles stop growing and disintegrate. Follicular development occurs because of a rise in the blood level of (FSH), which is secreted by the . The maturing follicle releases , the level of which rises throughout the follicular phase. You can see these and other changes in hormone levels that occur during the menstrual cycle in the following chart.
Ovulation
is the second phase of the . It usually occurs around day 14 of a 28-day menstrual cycle. During this phase, the Graafian follicle ruptures and releases its ovum. Ovulation is stimulated by a sudden rise in the blood level of (LH) from the . This is called the LH surge. You can see the LH surge in the top hormone graph in Figure 18.8.3. The LH surge generally starts around day 12 of the cycle and lasts for a day or two. The surge in LH is triggered by a continued rise in estrogen from the maturing follicle in the ovary. During the , the rising estrogen level actually suppresses LH secretion by the pituitary gland. However, by the time the follicular phase is nearing its end, the level of estrogen reaches a threshold level above which this effect is reversed, and stimulates the release of a large amount of LH. The surge in LH matures the ovum and weakens the wall of the follicle, causing the fully developed follicle to release its secondary .
Luteal Phase
The is the third and final phase of the ovarian cycle. It typically lasts about 14 days in a 28-day menstrual cycle. At the beginning of the luteal phase, and cause the Graafian follicle that ovulated the egg to transform into a structure called a . The corpus luteum secretes , which in turn suppresses FSH and LH production by the pituitary gland and stimulates the continued buildup of the in the uterus. How this phase ends depends on whether or not the ovum has been fertilized.
- If fertilization has not occurred, the falling levels of FSH and LH during the luteal phase cause the corpus luteum to atrophy, so its production of progesterone declines. Without a high level of progesterone to maintain it, the endometrium starts to break down. By the end of the luteal phase, the endometrium can no longer be maintained, and the next menstrual cycle begins with the shedding of the endometrium (menses).
- If has occurred so a forms and then divides to become a , the outer layer of the blastocyst produces a hormone called (HCG). This hormone is very similar to LH and preserves the corpus luteum. The corpus luteum can then continue to secrete progesterone to maintain the new pregnancy.
Uterine Cycle
The events of the that take place in the uterus make up the . This cycle consists of changes that occur mainly in the , which is the layer of tissue that lines the uterus. The uterine cycle is divided into the following three phases: menstruation, proliferative phase, and secretory phase. These phases are illustrated in Figure 18.8.4.
Menstruation
(also called menstrual period or menses) is the first phase of the uterine cycle. It occurs if has not taken place during the preceding menstrual cycle. During menstruation, the of the uterus, which has built up during the preceding cycle, degenerates and is shed from the , flowing through an opening in the cervix, and out through the external opening of the vagina. The average loss of blood during menstruation is about 35 mL (about 1 oz or 2 tablespoons). The flow of blood is often accompanied by uterine cramps, which may be severe in some women.
Proliferative Phase
The is the second phase of the uterine cycle. During this phase, secreted by cells of the maturing causes the lining of the uterus to grow, or proliferate. Estrogen also stimulates the of the uterus to secrete larger amounts of thinner mucus that can help swim through the cervix and into the uterus, making fertilization more likely.
Secretory Phase
The is the third and final phase of the . During this phase, produced by the in the ovary stimulates further changes in the so it is more receptive to implantation of a . For example, progesterone increases blood flow to the uterus and promotes uterine secretions. It also decreases the contractility of tissue in the uterine wall.
Bringing it All Together
It is important to note that the pituitary gland, the ovaries and the uterus are all responsible for parts of the ovarian and uterine cycles. The pituitary hormones, LH and FSH affect the ovarian cycle and its hormones. The ovarian hormones, estrogen and progesterone affect the uterine cycle and also feedback on the pituitary gland. Look at Figure 18.8.5 and look at what is happening on different days of the cycle in each of the sets of hormones, the ovarian cycle and the uterine cycle.
18.8 Summary
- The refers to natural changes that occur in the female reproductive system each month during the reproductive years, except when a woman is pregnant. The cycle is necessary for the production of ova and the preparation of the for . It involves changes in both the and uterus, and is controlled by hormones ( and ) and ovarian hormones ( and ).
- The female reproductive period is delineated by , or the first menstrual period, which usually occurs around age 12 or 13; and by , or the cessation of menstrual periods, which typically occurs around age 52. A typical menstrual cycle averages 28 days in length but may vary normally from 21 to 45 days. The average menstrual period is five days long, but may vary normally from two to seven days. These variations in the menstrual cycle may occur both between women and within individual women from month to month.
- The events of the menstrual cycle that take place in the ovaries make up the . It includes the (when a and its ovum mature due to rising levels of FSH), (when the is released from the ovary due to a rise in estrogen and a surge in LH), and the (when the follicle is transformed into a structure called a corpus luteum that secretes progesterone). In a 28-day menstrual cycle, the follicular and luteal phases typically average about two weeks in length, with ovulation generally occurring around day 14 of the cycle.
- The events of the that take place in the make up the uterine cycle. It includes , which generally occurs on days 1 to 5 of the cycle and involves shedding of endometrial tissue that built up during the preceding cycle; the , during which the endometrium builds up again until occurs; and the , which follows ovulation and during which the endometrium secretes substances and undergoes other changes that prepare it to receive an .
18.8 Review Questions
- What is the menstrual cycle? Why is the menstrual cycle necessary in order for pregnancy to occur?
- What organs are involved in the menstrual cycle?
- Identify the two major events that mark the beginning and end of the reproductive period in females. When do these events typically occur?
- Discuss the average length of the menstrual cycle and menstruation, as well as variations that are considered normal.
- If the LH surge did not occur in a menstrual cycle, what do you think would happen? Explain your answer.
- Give one reason why FSH and LH levels drop in the luteal phase of the menstrual cycle.
18.8 Explore More
https://youtu.be/cjbgZwgdY7Q
Why do women have periods? TED-Ed, 2015.
https://youtu.be/5B3Abpv0ysM
Girl's Rite of Passage | National Geographic, 2007.
Attributions
Figure 18.8.1
WaterforPeople_Uganda by WaterforPeople_Uganda on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 18.8.2
Ovarian Cycle by CNX OpenStax on Wikimedia Commons is used and adapted under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.
Figure 18.8.3
Figure_43_04_04 by CNX OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license. (Original: modification of work by Mikael Häggström)
Figure 18.8.4
Ovarian and menstrual cycle by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.8.5
1000px-MenstrualCycle2_en.svg by Isometrik on Wikimedia Common is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 27.15 Hormone levels in ovarian and menstrual cycles [digital image]. In Anatomy and Physiology (Section 27.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/27-2-anatomy-and-physiology-of-the-female-reproductive-system
National Geographic. (2007, May 31). Girl's rite of passage | National Geographic. YouTube. https://www.youtube.com/watch?v=5B3Abpv0ysM&feature=youtu.be
OpenStax. (2016, May 27) Figure 4 Rising and falling hormone levels result in progression of the ovarian and menstrual cycles [digital image]. In Open Stax, Biology (Section 43.4). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:Ha3dnFEx@6/Hormonal-Control-of-Human-Reproduction
TED-Ed. (2015, October 19). Why do women have periods? YouTube. https://www.youtube.com/watch?v=cjbgZwgdY7Q&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Vaccinating Against Cancer
Can a vaccine prevent? In the case of cervical cancer, it can. Cervical cancer is one of three disorders of the female reproductive system described in detail in this concept. Of the three, only cervical cancer can be prevented with a vaccine.
Cervical Cancer
occurs when cells of the (neck of the ) grow abnormally and develop the ability to invade nearby tissues or spread to other parts of the body, such as the abdomen or lungs. Figure 18.9.2 shows the location of the and the appearance of normal and abnormal cervical cells when examined with a microscope.
Cervical Cancer Prevalence and Death Rates
Worldwide, cervical is the second most common type of cancer in females (after breast cancer) and the fourth-most common cause of cancer death in females. In Canada and other high-income nations, the widespread use of cervical cancer screening has detected many cases of precancerous cervical changes and has dramatically reduced rates of cervical cancer deaths. About 75% of cervical cancer cases occur in developing countries, where routine screening is less likely because of cost and other factors. Cervical cancer is also the most common cause of cancer death in low-income countries.
Symptoms of Cervical Cancer
Early in the development of cervical cancer, there are typically no symptoms. As the disease progresses, however, symptoms are likely to occur. The symptoms may include abnormal vaginal bleeding, pelvic pain, or pain during sexual intercourse. Unfortunately, by the time symptoms start to occur, cervical cancer has typically progressed to a stage at which treatment is less likely to be successful.
Cervical Cancer Causes and Risk Factors
More than 90 per cent of cases of cervical cancer are caused at least in part by (HPV), which is a sexually transmitted virus that also causes genital warts. Figure 18.9.3 shows how HPV infection can cause cervical cancer by interfering with a normal cell division checkpoint. When HPV is not present, cervical cells containing mutations are not allowed to divide, so the cervix remains healthy. When HPV is present, however, cervical cells with mutations may be allowed to divide, leading to uncontrolled growth of mutated cells and the formation of a tumor.
Other risk factors for cervical cancer include smoking, a weakened immune system (for example, due to HIV infection), use of birth control pills, becoming sexually active at a young age, and having many sexual partners. However, these risk factors are less important than HPV infection. Instead, the risk factors are more likely to increase the risk of cervical cancer in females who are already infected with HPV. For example, among HPV-infected women, current and former smokers have roughly two to three times the incidence of cervical cancer as non-smokers. Passive smoking, or secondhand smoke, is also associated with an increased risk of cervical cancer, but to a lesser extent.
Diagnosis of Cervical Cancer
Diagnosis of cervical cancer is typically made by looking for microscopic abnormal cervical cells in a smear of cells scraped off the cervix. This is called a . If cancerous cells are detected or suspected in the smear, this test is usually followed up with a biopsy to confirm the Pap smear results. Medical imaging (by CT scan or MRI, for example) is also likely to be done to provide more information, such as whether the cancer has spread.
Prevention of Cervical Cancer
It is now possible to prevent HPV infection with a vaccine. The first HPV vaccine was approved by the U.S. Food and Drug Administration in 2006. The protects against the strains of HPV that have the greatest risk of causing cervical cancer. It is thought that widespread use of the vaccine will prevent up to 90% of cervical cancer cases. Current recommendations are for females to be given the vaccine between the ages of nine and 26. (Boys should be vaccinated against HPV, as well, because the virus may also cause cancer of the penis and certain other male cancers.) The vaccine is effective only if it is given before HPV infection has occurred. Using condoms during sexual intercourse can also help prevent HPV infection and cervical cancer, in addition to preventing pregnancy and sexually transmitted infections (such as HIV).
Even in women who have received the HPV vaccine, there is still a small risk of developing cervical cancer. Therefore, it is recommended that women continue to be examined with regular Pap smears.
Treatment of Cervical Cancer
Treatment of cervical cancer generally depends on the stage at which the cancer is diagnosed, but it is likely to include some combination of surgery, radiation therapy, and/or . Outcomes of treatment depend largely on how early the cancer is diagnosed and treated. For surgery to cure cervical cancer, the entire tumor must be removed with no cancerous cells found at the margins of the removed tissue on microscopic examination. If cancer is found and treated very early when it is still in the microscopic stage, the five-year survival rate is virtually 100%.
Vaginitis
is inflammation of the vagina — and sometimes the , as well. Symptoms may include a discharge that is yellow, gray, or green; itching; pain; and a burning sensation. There may also be a foul vaginal odor and pain or irritation with .
Causes of Vaginitis
About 90% of cases of vaginitis are caused by infection with . Most commonly, vaginal infections are caused by the yeast Candida albicans (see Figure 18.9.4). Such infections are referred to as vaginal or more commonly as a yeast infection. Candida albicans is one of the most common opportunistic infections in the world and can affect not only the vagina, but any of the mucus membranes and skin. Other possible causes of vaginal infections include bacteria, especially Gardnerella vaginalis, and some single-celled parasites, notably the protist parasite Trichomonas vaginalis, which is usually transmitted through vaginal intercourse. The risk of vaginal infections may be greater in women who wear tight clothing, are taking antibiotics for another condition, use birth control pills, or have improper hygiene. Poor hygiene allows organisms that are normally present in the stool (such as yeast) to contaminate the vagina.
Most of the remaining cases of vaginitis are due to irritation by — or allergic reactions to — various products. These irritants may include condoms, spermicides, soaps, douches, lubricants, and even semen. Using tampons or soaking in hot tubs may be additional causes of this type of vaginitis.
Diagnosis of Vaginitis
Diagnosis of typically begins with symptoms reported by the patient. This may be followed by a microscopic examination or culture of the vaginal discharge in order to identify the specific cause. The colour, consistency, acidity, and other characteristics of the discharge may be predictive of the causative agent. For example, infection with Candida albicans may cause a cottage cheese-like discharge with a low , whereas infection with Gardnerella vaginalis may cause a discharge with a fish-like odor and a high pH.
Prevention of Vaginitis
Prevention of vaginitis includes wearing loose cotton underwear that helps keep the dry. Yeasts and bacteria that may cause vaginitis tend to grow best in a moist environment. It is also important to avoid the use of perfumed soaps, personal hygiene sprays, and douches, all of which may upset the normal pH and bacterial balance in the vagina. To help avoid vaginitis caused by infection with Trichomonas vaginalis, the use of condoms during sexual intercourse is advised.
Treatment of Vaginitis
The appropriate treatment of vaginitis depends on the cause. In many cases of vaginitis, there is more than one cause, and all of the causes must be treated to ensure a cure.
- Yeast infections of the vagina are typically treated with topical anti-fungal medications, which are available over the counter. The medications may be in the form of tablets or creams that are inserted into the vagina. Depending on the particular medication used, treatment may involve one, three, or seven days of applications.
- Bacterial infections of the vagina are usually treated with antibiotics. These may be taken orally as pills, or applied topically to the vagina in creams.
- Trichomonas vaginalis infections of the vagina are generally treated with a single dose of an oral antibiotic. Sexual partners should be treated at the same time, and intercourse should be avoided for at least a week until both partners have completed treatment, and have been followed-up by a physician.
Endometriosis
is a disease in which endometrial tissue, which normally grows inside the uterus, grows outside it, as shown in Figure 18.9.5. Most often, the endometrial tissue grows around the ovaries, Fallopian tubes, and uterus. In rare instances, the tissue may grow elsewhere in the body. The areas of endometriosis typically bleed each month during the menstrual period, and this often results in inflammation, pain, and scarring. An estimated six to ten per cent of women are believed to have endometriosis. It is most common in women during their thirties and forties, and only rarely occurs before menarche or after menopause.
Signs and Symptoms of Endometriosis
The main symptom of is pelvic pain, which may range from mild to severe. There appears to be little or no relationship between the amount of endometrial tissue growing outside the uterus and the severity of the pain. For many women with the disease, the pain occurs mainly during . However, nearly half of those affected have chronic pelvic pain. The pain of endometriosis may be caused by bleeding in the pelvis, which triggers . Pain can also occur from internal scar tissue that binds internal organs to each other.
Another problem often associated with endometriosis is infertility, or the inability to conceive or bear children. Among women with endometriosis, up to half may experience infertility. Infertility can be related to scar formation or to anatomical distortions due to the abnormal endometrial tissue. Other possible symptoms of endometriosis may include diarrhea or constipation, chronic fatigue, nausea and vomiting, headaches, and heavy or irregular menstrual bleeding.
Causes of Endometriosis
The causes of endometriosis are not known for certain, but several risk factors have been identified, including a family history of endometriosis. Daughters or sisters of women with endometriosis have about six times the normal risk of developing the disease themselves. It has been suggested that endometriosis results from in several s. It is likely that endometriosis is multifactorial, involving the interplay of several factors.
At the physiological level, the predominant idea for how endometriosis comes about is retrograde menstruation. This happens when some of the endometrial debris from a woman’s menstrual flow exits the through the , rather than through the . The debris then attaches itself to the outside of organs in the abdominal cavity, or to the lining of the abdominal cavity itself. Retrograde menstruation, however, does not explain all cases of endometriosis, so other factors are apparently involved. Suggestions include environmental toxins and responses.
Diagnosis of Endometriosis
Diagnosis of endometriosis is usually based on self-reported symptoms and a physical examination by a doctor, often combined with medical imaging, such as ultrasonography. The only way to definitively diagnose endometriosis, however, is through visual inspection of the endometrial tissue. This can be done with a surgical procedure called laparoscopy, shown in Figure 18.9.6, in which a tiny camera is inserted into the abdomen through a small incision. The camera allows the physician to visually inspect the area where endometrial tissue is suspected.
Treatment of Endometriosis
The most common treatments for endometriosis are medications to control the pain, and surgery to remove the abnormal tissue. Frequently used pain medications are non-steroidal inflammatory drugs (), such as naproxen. Opiates may be used in cases of severe pain. Laparoscopy can be used to surgically treat endometriosis, as well as to diagnose the condition. In this type of surgery, an additional small incision is made to insert instruments that the surgeon can manipulate externally in order to burn (cauterize) or cut away the endometrial growths. In younger women who want to have children, surgery is conservative to keep the reproductive organs intact and functional. However, with conservative surgery, endometriosis recurs in 20–40% of cases within five years of the surgery. In older women who have completed childbearing, may be undertaken to remove all or part of the internal reproductive organs. This is the only procedure that is likely to cure endometriosis and prevent relapses.
Feature: My Human Body
A is a method of cervical cancer screening used to detect potentially pre-cancerous and cancerous cells in the . It is the most widely used screening test for this type of cancer, and it is very effective. The test may also detect vaginal infections and abnormal endometrial cells, but it is not designed for these purposes.
According to HealthLink BC, females should start receiving routine Pap smears by age 25. Because most cases of cervical cancer are caused by infection with , which is a sexually transmitted infection, there is little or no benefit to screening people who have not had sexual contact. Starting at age 25, general guidelines are for Pap smears to be repeated every three years until age 69. Screening may be discontinued after 69 years of age, if the last three Pap smears were normal. If a woman has a complete , she no longer has a cervix and there is no need for further Pap smears. On the other hand, if a woman has had a history of abnormal Pap smears or , she will likely be screened more frequently. Pap smears can be done safely during the first several months of pregnancy, and resumed about three months after childbirth. Generally, better results are obtained if Pap smears are not done during menstruation.
If you’ve never had a Pap smear, knowing what to expect may help prepare you for the procedure. The patient lies on the examining table with her feet in “stirrups” to hold the legs up and apart. An instrument called a speculum is inserted into the vagina to hold back the vaginal walls and give access to the cervix. A tiny amount of tissue is brushed off the cervix and smeared onto a microscope slide. The speculum is then removed, and the procedure is over. The slide is later examined under a microscope for abnormal cells. Some women experience light spotting or mild diarrhea after a Pap smear, but most have no lasting effects.
Pap smears are uncomfortable and may be somewhat painful for some women. If you experience pain during a Pap smear, tell your health care provider. Many steps can be taken to minimize the pain, which might include using a smaller speculum, using warm instruments and a lubricant, and applying a topical anesthetic such as lidocaine to the cervix before obtaining the smear. Any pain is generally very brief, and the potential reward is worth it. Pap tests are estimated to reduce up to 80% of cervical cancer deaths. One of the lives saved could be your own.
18.9 Summary
- occurs when cells of the cervix grow abnormally and develop the ability to invade nearby tissues or spread to other parts of the body. Worldwide, cervical cancer is the second-most common type of in females and the fourth-most common cause of cancer death in females. Early on, cervical cancer often has no symptoms. Later, symptoms (such as abnormal vaginal bleeding and pain) are likely.
- Most cases of cervical cancer occur because of infection with , so the HPV vaccine is expected to greatly reduce the incidence of the disease. Other risk factors include smoking and a weakened immune system. A can diagnose cervical cancer at an early stage. Where Pap smears are done routinely, cervical cancer death rates have fallen dramatically. Treatment of cervical cancer generally includes surgery, which may be followed by radiation therapy or chemotherapy.
- is inflammation of the vagina. A discharge is likely, and there may be itching and pain. About 90% of cases of vaginitis are caused by infection with , typically by the yeast Candida albicans. A minority of cases are caused by irritants or allergens in soaps, spermicides, or douches.
- Diagnosis of vaginitis may be based on characteristics of the discharge, which can be examined microscopically or cultured. Treatment of vaginitis depends on the cause and is usually an oral or topical anti-fungal or antibiotic medication.
- is a disease in which endometrial tissue grows outside the . This tissue may bleed during the and cause inflammation, pain, and scarring. The main symptom of endometriosis is pelvic pain, which may be severe. Endometriosis may also lead to .
- Endometriosis is thought to have multiple causes, including genetic mutations. Retrograde menstruation may be the immediate cause of endometrial tissue escaping the uterus and entering the pelvic cavity. Endometriosis is usually treated with surgery to remove the abnormal tissue and medication for pain. If surgery is more conservative than hysterectomy, endometriosis may recur.
18.9 Review Questions
- What is cervical cancer? Worldwide, how prevalent is it, and how does it rank as a cause of cancer deaths?
- Identify symptoms of cervical cancer. What are causes of — and risk factors for — cervical cancer?
- What roles can Pap smears and HPV vaccines play in preventing cervical cancer cases and cervical cancer deaths?
- How is cervical cancer treated?
- Define vaginitis and identify its symptoms.
- What are some of the causes of vaginitis? Which cause is responsible for most of the cases?
- How is vaginitis diagnosed and treated?
- What is endometriosis, and what are its symptoms?
- Discuss possible causes of endometriosis.
- How is endometriosis treated? Which treatment is most likely to prevent recurrence of the disorder?
- In the case of infection with Trichomonas vaginalis, why is the woman’s sexual partner usually treated at the same time?
18.9 Explore More
https://youtu.be/KOz-bNhEHhQ
What is HPV and how can you protect yourself from it? - Emma Bryce, TED-Ed, 2019.
https://youtu.be/6HeQ4iEqAUk
Endometriosis - The Mystery Disease of Women | Cécile Real | TEDxBinnenhof, TEDx Talks, 2016.
https://youtu.be/ryNjSP5VVI8
The brain and ovarian hormones | Marwa Azab | TEDxMontrealWomen, TEDxTalks, 2015.
Attributions
Figure 18.9.1
a-nurse-giving-a-young-girl-a-vaccine-shot-or by CDC/ Judy Schmidt from Public Health Image Library (PHIL) #9424 is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 18.9.2
1024px-Blausen_0221_CervicalDysplasia by Blausen Medical Communications, Inc. on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.9.3
HPV and Cervical Cancer by OpenStax by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.9.4
Candida by NIH on Flickr from the NIH Image Gallery on Flickr is used under a CC BY NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 18.9.5
Blausen_0349_Endometriosis by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.9.6
1024px-Blausen_0602_Laparoscopy_02 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 27.16 Development of cervical cancer [digital image]. In Anatomy and Physiology (Section 27.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/27-2-anatomy-and-physiology-of-the-female-reproductive-system
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
HealthLink BC. (n.d.). Pap test: British Columbia specific information. https://www.healthlinkbc.ca/medical-tests/hw5266
TED-Ed. (2019, July 9). What is HPV and how can you protect yourself from it? - Emma Bryce. YouTube. https://www.youtube.com/watch?v=KOz-bNhEHhQ&feature=youtu.be
TEDx Talks. (2016, April 14). Endometriosis - The mystery disease of women | Cécile Real | TEDxBinnenhof. YouTube. https://www.youtube.com/watch?v=6HeQ4iEqAUk&feature=youtu.be
TEDx Talks. (2015, July 27). The brain and ovarian hormones | Marwa Azab | TEDxMontrealWomen. YouTube. https://www.youtube.com/watch?v=ryNjSP5VVI8&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Figure 18.10.1 Families all have something in common.
Family Portrait
What do all these families (Figure 18.10.1) have in common? They were born! Every person on this planet was conceived, carried in utero and then born. While families come in all shapes, sizes and styles, we all came into existence in the same way. Virtually all human societies past and present — value having children. Indeed, for many people, parenthood is an important life goal. Unfortunately, some people are unable to achieve that goal because of infertility.
What Is Infertility?
is the inability of a sexually mature adult to reproduce by natural means. For scientific and medical purposes, infertility is generally defined as the failure to achieve a successful pregnancy after at least one year of regular, unprotected sexual intercourse. Infertility may be primary or secondary. Primary infertility applies to cases in which an individual has never achieved a successful pregnancy. Secondary infertility applies to cases in which an individual has had at least one successful pregnancy, but fails to achieve another after trying for at least a year. Infertility is a common problem. The government of Canada reported that in 2019, 16% of Canadian couples experience infertility, a number which has doubled since the 1980s. If you look around at the couples you know, that means that almost 1 in 6 of them are having issues with fertility.
Causes of Infertility
is the result of a multi-step process. In order for a normal pregnancy to occur, a woman must release an from one of her , the ovum must go through an , a man’s must fertilize the ovum as it passes through the oviduct, and then the resulting must implant in the . If there is a problem with any of these steps, can result.
A couple’s infertility may be due to a problem with either the male or the female partner. As shown in the circle graph below (Figure 18.10.2), about 40% of infertility cases are due to female infertility, and about 30% are due to male infertility. The remaining 30% of cases are due to a combination of male and female problems or unknown causes.
Causes of Male Infertility
Male infertility occurs when there are no, or too few, , or when the sperm are not healthy and motile and cannot travel through the female reproductive tract to fertilize an egg. A common cause of inadequate numbers or motility of sperm is varicocele, which is enlargement of blood vessels in the . This may raise the temperature of the and adversely affect sperm production. In other cases, there is no problem with the sperm, but there is a blockage in the male reproductive tract that prevents the sperm from being ejaculated.
Factors that increase a man’s risk of infertility include heavy alcohol use, drug abuse, cigarette smoking, exposure to environmental toxins (such as pesticides or lead), certain medications, serious diseases (such as kidney disease), and radiation or chemotherapy for cancer. Another risk factor is advancing age. Male fertility normally peaks in the mid-twenties and gradually declines after about age 40, although it may never actually drop to zero.
Causes of Female Infertility
Female infertility generally occurs due to one of two problems: failure to produce viable by the , or structural problems in the or . The most common cause of female infertility is a problem with . Without ovulation, there are no ova to be fertilized. Anovulatory cycles (menstrual cycles in which ovulation does not occur) may be associated with no or irregular menstrual periods, but even regular menstrual periods may be anovulatory for a variety of reasons. The most common cause of anovulatory cycles is , which causes hormone imbalances that can interfere with normal ovulation. Another relatively common cause of anovulation is primary ovarian insufficiency. In this condition, the ovaries stop working normally and producing viable eggs at a relatively early age, generally before the age of 40.
Structural problems with the oviducts or uterus are less common causes of female infertility. The oviducts may be blocked as a result of . Another possible cause is pelvic inflammatory disease, which occurs when sexually transmitted infections spread to the oviducts or other female reproductive organs (see Figure 18.10.3). The infection may lead to scarring and blockage of the oviducts. If an ovum is produced and the oviducts are functioning — and a woman has a condition such as uterine fibroids — implantation in the uterus may not be possible. Uterine fibroids are non-cancerous clumps of tissue and muscle that form on the walls of the uterus.
Factors that increase a woman’s risk of infertility include tobacco smoking, excessive use of alcohol, stress, poor diet, strenuous athletic training, and being overweight or underweight. Advanced age is even more problematic for females than males. Female fertility normally peaks in the mid-twenties, and continuously declines after age 30 and until menopause around the age of 52, after which the ovary no longer releases eggs. About 1/3 of couples in which the woman is over age 35 have fertility problems. In older women, more cycles are likely to be anovulatory, and the eggs may not be as healthy.
Diagnosing Causes of Infertility
Diagnosing the cause(s) of a couple’s infertility often requires testing both the man and the woman for potential problems. In men, the is likely to be examined for the number, shape, and motility of sperm. If problems are found with sperm, further studies are likely to be done, such as medical imaging to look for structural problems with the testes or ducts.
In women, the first step is most often determining whether is occurring. This can be done at home by carefully monitoring body temperature (it rises slightly around the time of ovulation) or using a home ovulation test kit, which is available over the counter at most drugstores. Whether or not ovulation is occurring can also be detected with blood tests or ultrasound imaging of the ovaries. If ovulation is occurring normally, then the next step may be an X-ray of the oviducts and uterus to see if there are any blockages or other structural problems. Another approach to examining the female reproductive tract for potential problems is laparoscopy. In this surgical procedure, a tiny camera is inserted into the woman’s abdomen through a small incision. This allows the doctor to directly inspect the reproductive organs.
Treating Infertility
Infertility often can be treated successfully. The type of treatment depends on the cause of infertility.
Treating Male Infertility
Medical problems that interfere with sperm production may be treated with medications or other interventions that may lead to the resumption of normal sperm production. If, for example, an infection is interfering with sperm production, then antibiotics that clear up the infection may resolve the problem. If there is a blockage in the male reproductive tract that prevents the of sperm, surgery may be able to remove the blockage. Alternatively, the man’s sperm may be removed from his body and then used for artificial insemination of his partner. In this procedure, the sperm are injected into the woman’s reproductive tract.
Treating Female Infertility
In females, it may be possible to correct blocked Fallopian tubes or uterine fibroids with surgery. Ovulation problems, on the other hand, are usually treated with hormones that act either on the or on the ovaries. Hormonal treatments that stimulate ovulation often result in more than one egg being ovulated at a time, thus increasing the chances of a woman having twins, triplets, or even higher multiple births. Multiple fetuses are at greater risk of being born too early or having health and developmental problems. The mother is also at greater risk of complications arising during pregnancy. Therefore, the possibility of multiple fetuses should be weighed in making a decision about this type of infertility treatment.
Assisted Reproductive Technology
Some cases of infertility are treated with . This is a collection of medical procedures in which ova are removed from the woman’s body and sperm are taken from the man’s body to be manipulated in ways that increase the chances of fertilization occurring. The eggs and sperm may be injected into one of the woman’s oviducts for fertilization to take place in vivo (in the body). More commonly, however, the eggs and sperm are mixed together outside the body so fertilization takes place in vitro (in a test tube or dish in a lab). The latter approach is illustrated in Figure 18.10.4. With in vitro fertilization, the fertilized eggs may be allowed to develop into embryos before being placed in the woman’s uterus.
ART has about a 40% chance of leading to a live birth in women under the age of 35, but only about a 20%t chance of success in women over the age of 35. Some studies have found a higher-than-average risk of birth defects in children produced by ART procedures, but this may be due to the generally higher ages of the parent — not the technologies used.
Other Approaches
Other approaches for certain causes of infertility include the use of a surrogate mother, a gestational carrier, or sperm donation.
- A surrogate mother is a woman who agrees to become pregnant using the man’s sperm and her own egg. The child, who will be the biological offspring of the surrogate and the male partner, is given up at birth for adoption by the couple. Surrogacy might be selected by women with no eggs or unhealthy eggs. A woman who carries a mutant gene for a serious genetic disorder might choose this option to ensure that the defective gene is not passed on to the offspring.
- A gestational carrier is a woman who agrees to receive a transplanted embryo from a couple and carry it to term. The child, who will be the biological offspring of the couple, is given to the parents at birth. A gestational carrier might be used by women who have normal ovulation but no uterus, or who cannot safely carry a fetus to term because of a serious health problem (such as kidney disease or cancer).
- Sperm donation is the use of sperm from a fertile man (generally through artificial insemination) for cases in which the male partner in a couple is infertile, or in which a woman seeks to become pregnant without a male partner. A lesbian couple may use donated sperm to enable one of them to become pregnant and have a child. Sperm can be obtained from a sperm bank, which buys and stores sperm for artificial insemination, or a male friend or other individual may donate sperm to a specific woman.
Social and Ethical Issues Relating to Infertility
For people who have a strong desire for children of their own, infertility may lead to deep disappointment and depression. Individuals who are infertile may even feel biologically inadequate. Partners in infertile couples may argue and feel resentment toward each other, and married couples may get divorced because of infertility. Infertility treatments — especially ART procedures — are generally time-consuming and expensive. The high cost of the treatments can put them out of financial reach of many couples.
Ethical Concerns
Some people question whether the allocation of medical resources to infertility treatments is justified, and whether the resources could be better used in other ways. The status of embryos that are created in vitro and then not used for a pregnancy is another source of debate. Some people oppose their destruction on religious grounds, and couples may sometimes argue about what should be done with their extra embryos. Ethical issues are also raised by procedures that increase the chances of multiple births, because of the medical and developmental risks associated with multiple births.
Infertility in Developing Countries
Infertility is an under-appreciated problem in the poorer nations of the world, because of assumptions about overpopulation problems and high birth rates in developing countries. In fact, infertility is at least as great a problem in developing as in developed countries. High rates of health problems and inadequate health care in the poorer nations increase the risk of infertility. At the same time, infertility treatments are usually not available — or are far too expensive — for the vast majority of people who may need them. In addition, in many developing countries, the production of children is highly valued. Children may be needed for family income generation and economic security of the elderly. It is not uncommon for infertility to lead to social stigmatization, psychological problems, and abandonment by spouses.
18.10 Summary
- is the inability of a sexually mature adult to reproduce by natural means. It is defined scientifically and medically as the failure to achieve a successful pregnancy after at least one year of regular, unprotected sexual intercourse.
- About 40% of infertility in couples is due to female infertility, and another 30% is due to male infertility. In the remaining cases, a couple’s infertility is due to problems in both partners, or to unknown causes.
- Male infertility occurs when there are no, or too few, healthy, motile . This may be caused by problems with , or by blockage of the male reproductive tract that prevents sperm from being ejaculated. Risk factors for male infertility include heavy alcohol use, smoking, certain medications, and advancing age, to name just a few.
- Female infertility occurs due to failure to produce viable ova by the ovaries, or structural problems in the oviducts or uterus. Polycystic ovary syndrome (PCOS) is the most common cause of failure to produce viable ova. and uterine fibroids are possible causes of structural problems in the oviducts and uterus. Risk factors for female infertility include smoking, stress, poor diet, and older age, among others.
- Diagnosing the cause(s) of a couple’s infertility generally requires testing both the man and the woman for potential problems. For men, semen is likely to be examined for adequate numbers of healthy, motile sperm. For women, signs of ovulation are monitored, for example, with an ovulation test kit or ultrasound of the ovaries. For both partners, the reproductive tract may be medically imaged to look for blockages or other abnormalities.
- Treatments for infertility depend on the cause. For example, if a medical problem is interfering with sperm production, medication may resolve the underlying problem so sperm production is restored. Blockages in either the male or the female reproductive tract can often be treated surgically. If there are problems with ovulation, hormonal treatments may stimulate ovulation.
- Some cases of infertility are treated with . This is a collection of medical procedures in which ova and sperm are taken from the couple and manipulated in a lab to increase the chances of fertilization occurring and an embryo forming. Other approaches for certain causes of infertility include the use of a surrogate mother, gestational carrier, or sperm donation.
- Infertility can negatively impact a couple socially and psychologically, and it may be a major cause of marital friction or even divorce. Infertility treatments may raise ethical issues relating to the costs of the procedures and the status of embryos that are created in vitro, but not used for pregnancy. Infertility is an under-appreciated problem in developing countries, where birth rates are high and children have high economic — as well as social — value. In these countries, poor health care is likely to lead to more problems with infertility and fewer options for treatment.
18.10 Review Questions
- What is infertility? How is infertility defined scientifically and medically?
- What percentage of infertility in couples is due to male infertility? What percentage is due to female infertility?
- Identify causes of and risk factors for male infertility.
- Identify causes of and risk factors for female infertility.
- How are causes of infertility in couples diagnosed?
- How is infertility treated?
- Discuss some of the social and ethical issues associated with infertility or its treatment.
- Why is infertility an under-appreciated problem in developing countries?
- Describe two similarities between causes of male and female infertility.
- Explain the difference between males and females in terms of how age affects fertility.
- Do you think that taking medication to stimulate ovulation is likely to improve fertility in cases where infertility is due to endometriosis? Explain your answer.
18.10 Explore More
https://youtu.be/P27waC05Hdk
How in vitro fertilization (IVF) works - Nassim Assefi and Brian A. Levine, TED-Ed, 2015
https://youtu.be/6BBmMtVfZ4Y
A journey through infertility -- over terror's edge | Camille Preston | TEDxBeaconStreet, TEDx Talks, 2014.
https://youtu.be/iqA8uAjvEdM
Smoking Marijuana May Lower Sperm Count by 33%, David Pakman Show, 2015.
https://youtu.be/V6-v4eF9dyA
ivf embryo developing over 5 days by fertility Dr Raewyn Teirney, Fertility Specialist Sydney, 2014.
https://youtu.be/4Khn_z9FPmU
Homosexuality: It's about survival - not sex | James O'Keefe | TEDxTallaght, 2016.
Attributions
Figure 18.10.1
- Gay Pride Parade NYC 2013 - Happy Family by Bob Jagendorf on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
- #beaches #summer #family #blue #water by Jove Duero on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Photograph of five men near outdoor by Dollar Gill on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Família by Laercio Cavalcanti on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Happiness 🙂 by Ashwini Chaudhary on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 18.10.2
Causes of infertility in Canada by Christine Miller is in the Public Domain (https://creativecommons.org/publicdomain/mark/1.0/).
Figure 18.10.3
1024px-Blausen_0719_PelvicInflammatoryDisease by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 18.10.4
1024px-Blausen_0060_AssistedReproductiveTechnology 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.
David Pakman Show. (2015, September 1). Smoking marijuana may lower sperm count by 33%. YouTube. https://www.youtube.com/watch?v=iqA8uAjvEdM
Fertility Specialist Sydney. (2014, April 11). ivf embryo developing over 5 days by fertility Dr Raewyn Teirney. YouTube. https://www.youtube.com/watch?v=V6-v4eF9dyA&t=5s
Public Health Agency of Canada. (2019, May 28). Fertility. Government of Canada. https://www.canada.ca/en/public-health/services/fertility/fertility.html
TED-Ed. (2015, May 7). How in vitro fertilization (IVF) works - Nassim Assefi and Brian A. Levine. YouTube. https://www.youtube.com/watch?v=P27waC05Hdk&t=4s
TEDx Talks. (2014, June 26). A journey through infertility -- over terror's edge | Camille Preston | TEDxBeaconStreet. YouTube. https://www.youtube.com/watch?v=6BBmMtVfZ4Y&t=2s
TEDx Talks. (2016, November 15). Homosexuality: It's about survival - not sex | James O'Keefe | TEDxTallaght. YouTube. https://www.youtube.com/watch?v=4Khn_z9FPmU&t=1s
Created by CK-12 Foundation/Adapted by Christine Miller
Case Study Conclusion: Trying to Conceive
The woman in Figure 18.12.1 is holding a home pregnancy test. The two pink lines in the middle are the type of result that Alicia and Victor are desperately hoping to see themselves one day — a positive pregnancy test. In the beginning of the chapter you learned that Alicia and Victor have been actively trying to get pregnant for a year, which, as you now know, is the time frame necessary for infertility to be diagnosed.
Alicia and Victor tried having on day 14 of her to optimize their chances of having his meet her . Why might this not be successful, even if they do not have fertility problems? Although the average menstrual cycle is 28 days, with occurring around day 14, many women vary widely from these averages (either consistently or variably) from month to month. Recall, for example, that menstrual cycles may vary from 21 to 45 days in length, and a woman’s cycle is considered to be regular if it varies within as many as eight days from shortest to longest cycle. This variability means that ovulation often does not occur on or around day 14, particularly if the woman has significantly shorter, longer, or irregular cycles — like Alicia does. Therefore, by aiming for day 14 without knowing when Alicia is actually ovulating, they may not be successful in helping Victor’s sperm encounter Alicia’s egg.
Lack of ovulation entirely can also cause variability in menstrual cycle length. As you have learned, the regulation of the menstrual cycle depends on an interplay of from the and , including and from the pituitary and and from the ovary — specifically from the which surrounds the maturing egg and becomes the after ovulation. Shifts in these hormones and processes can affect ovulation and menstrual cycle length. This is why Alicia was concerned about her long and irregular menstrual cycles. If they are a sign that she is not ovulating, that could be the reason why she is having trouble getting pregnant.
In order to get a better idea of whether Alicia is ovulating, Dr. Bashir recommended that she take her basal body temperature (BBT) each morning before getting out of bed, and track it throughout her menstrual cycle. As you have learned, BBT typically rises slightly and stays high after ovulation. While tracking BBT is not a particularly effective form of contraception, since the temperature rise occurs only after ovulation, it can be a good way to see whether a woman is ovulating at all. Although not every woman will see a clear shift in BBT after ovulation, it is a relatively easy way to start assessing a woman’s fertility and is used as part of a more comprehensive fertility assessment by some physicians.
Dr. Bashir also recommended that Alicia use a home ovulation predictor kit. This is another relatively cheap and easy way to assess ovulation. Most ovulation predictor kits work by detecting the hormone LH in urine using test strips, like the ones shown in Figure 18.12.2. Why can this predict ovulation? Think about what you have learned about how ovulation is triggered. Rising levels of estrogen from the maturing follicle in the ovary causes a surge in the level of LH secreted from the pituitary gland, which triggers ovulation. This surge in LH can be detected by the home kit, which compares the level of LH in a woman’s urine to that of a control on the strip. After the LH surge is detected, ovulation will typically occur within one to two days.
By tracking her BBT and using the ovulation predictor kit, Alicia has learned that she is most likely ovulating, but not in every cycle, and sometimes she ovulates much later than day 14. Because frequent anovulatory cycles can be a sign of an underlying hormonal disorder, such as polycystic ovary syndrome (PCOS) or problems with the pituitary or other glands that regulate the reproductive system, Dr. Bashir orders blood tests for Alicia and sets up an appointment for a physical exam.
However, because Alicia is sometimes ovulating, the problem may not lie solely with her. Recall that infertility occurs in similar proportions in men and women, and can be due to problems in both partners. This is why it is generally recommended that both partners get assessed for fertility issues when they are having trouble getting pregnant after a year of trying.
Therefore, Victor proceeds with the analysis that Dr. Bashir recommended. In this process, the man provides a semen sample by ejaculating into a cup or special condom, and the semen is then examined under a microscope. The semen is then checked for sperm number, shape, and motility. Sperm with an abnormal shape or trouble moving will likely have trouble reaching and fertilizing an egg. A low number of sperm will also reduce the chances of conception. In this way, semen analysis can provide insight into the possible underlying causes of infertility. For instance, a low sperm count could indicate problems in sperm production or a blockage in the male reproductive tract that is preventing sperm from being emitted from the penis. Further testing would have to be done to distinguish between these two possible causes.
Victor had been worried that past injuries to his testes may have affected his fertility. You may remember the testes are where sperm are produced, and because they are external to the body, they are vulnerable to injury. In addition to physical damage to the testes and other parts of the male reproductive tract, a testicular injury could potentially cause the creation of antibodies against a man’s own sperm. As you have learned, lining the are tightly packed so that the developing sperm are normally well-separated from the body’s immune system. However, in the case of an injury, this barrier can be breached, which can cause the creation of antisperm antibodies. These antibodies can hamper fertility by killing the sperm, or otherwise interfering with their ability to move or fertilize an egg. When infertility is due to such antibodies, it is called “immune infertility.”
Victor’s semen analysis shows that he has normal numbers of healthy sperm. Dr. Bashir recommends that while they investigate whether Alicia has an underlying medical issue, she continue to track her BBT and use ovulation predictor kits to try to pinpoint when she is ovulating. She recommends that once Alicia sees an LH surge, the couple try to have intercourse within three days to maximize their chances of conception. If Alicia is found to have a medical problem that is inhibiting ovulation, depending on what it is, they may either address the problem directly, or she can take medication that stimulates ovulation, such as clomiphene citrate (often sold under the brand name Clomid). This medication works by increasing the amount of FSH secreted by the pituitary.
Fortunately, tracking ovulation at home and timing intercourse appropriately was all Alicia and Victor needed to do to finally get pregnant! After their experience, they, like you, now have a much deeper understanding of the intricacies of the reproductive system and the complex biology that is involved in the making of a new human organism.
Chapter 18 Summary
In this chapter, you learned about the male and female reproductive systems. Specifically, you learned that:
- The reproductive system is the human organ system responsible for the production and of and, in females, the carrying of a .
- Both male and female reproductive systems have organs called ( in males, in females) that produce gametes ( or ) and sex hormones (such as in males and in females). Sex hormones are endocrine hormones that control prenatal development of sex organs, sexual maturation at , and reproduction after puberty.
- The reproductive system is the only organ system that is significantly different between males and females. A Y-chromosome gene called SRY is responsible for undifferentiated embryonic tissues developing into a male reproductive system. Without a Y chromosome, the undifferentiated embryonic tissues develop into a female reproductive system.
- Male and female reproductive systems are different at birth, but immature and nonfunctioning. Maturation of the reproductive system occurs during puberty when hormones from the and pituitary gland stimulate the gonads to produce sex hormones again. The sex hormones, in turn, cause the physical changes experienced during puberty.
- Male reproductive system organs include the testes, , , , , and .
-
- The two testes are sperm- and testosterone-producing male gonads. They are contained within the , a pouch that hangs down behind the penis. The testes are filled with hundreds of tiny, tightly coiled seminiferous tubules, where sperm are produced. The tubules contain sperm in different stages of development, as well as Sertoli cells, which secrete substances needed for sperm production. Between the tubules are , which secrete testosterone.
- The two epididymides are contained within the scrotum. Each epididymis is a tightly coiled tubule where sperm mature and are stored until they leave the body during an .
- The two vas deferens are long, thin tubes that run from the scrotum up into the . During ejaculation, each vas deferens carries sperm from one of the epididymides to one of the pair of ejaculatory ducts.
- The two seminal vesicles are glands within the pelvis that secrete fluid through ducts into the junction of each vas deferens and ejaculatory duct. This alkaline fluid makes up about 70% of semen, the sperm-containing fluid that leaves the penis during ejaculation. Semen contains substances and nutrients that sperm need to survive and “swim” in the female reproductive tract.
- The prostate gland is located just below the seminal vesicles and surrounds the urethra and its junction with the ejaculatory ducts. The prostate secretes an alkaline fluid that makes up close to 30% of semen. Prostate fluid contains a high concentration of zinc, which sperm need to be healthy and motile.
- The ejaculatory ducts form where the vas deferens joins with the ducts of the seminal vesicles in the prostate gland. They connect the vas deferens with the urethra. The ejaculatory ducts carry sperm from the vas deferens, and secretions from the seminal vesicles and prostate gland that together form semen.
- The paired are located just below the prostate gland. They secrete a tiny amount of fluid into semen. The secretions help lubricate the urethra and neutralize any acidic urine it may contain.
- The penis is the external male organ that has the reproductive function of , which is delivering sperm to the female reproductive tract. The penis also serves as the organ that excretes urine. The urethra passes through the penis and carries urine or semen out of the body. Internally, the penis consists largely of columns of spongy tissue that can fill with blood and make the penis stiff and erect. This is necessary for so intromission can occur.
- Parts of a mature sperm include the , , , and . The process of producing sperm is called . This normally starts during puberty and continues uninterrupted until death.
-
- Spermatogenesis occurs in the seminiferous tubules in the testes, and requires high concentrations of testosterone. Sertoli cells in the testes play many roles in spermatogenesis, including concentrating testosterone under the influence of follicle stimulating hormone (FSH) from the pituitary gland.
- Spermatogenesis begins with a stem cell called a , which undergoes to produce a primary spermatocyte. The primary spermatocyte undergoes meiosis I to produce haploid secondary spermatocytes, and these cells in turn, undergo meiosis II to produce spermatids. After the spermatids grow a tail and undergo other changes, they become sperm.
- Before sperm are able to “swim,” they must mature in the epididymis. The mature sperm are then stored in the epididymis until ejaculation occurs.
- Ejaculation is the process in which semen is propelled by in the vas deferens and ejaculatory ducts from the urethra in the penis.
- Leydig cells in the testes secrete testosterone under the control of luteinizing hormone (LH) from the pituitary gland. Testosterone is needed for male sexual development at puberty and to maintain normal spermatogenesis after puberty. It also plays a role in prostate function and the ability of the penis to become erect.
- Disorders of the male reproductive system include (ED), , , and.
-
- ED is a disorder characterized by the regular and repeated inability of a sexually mature male to obtain and maintain an erection. ED is a common disorder that occurs when normal blood flow to the penis is disturbed or 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 and adopting a healthier diet and regular exercise. However, the first-line treatment 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.
- Epididymitis is inflammation of the epididymis. 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.
- Prostate cancer 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, a 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 no treatment may 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.
- Testicular cancer, 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. Normal male reproductive functions are still possible after one testis is removed, if the remaining testis is healthy.
-
- The female reproductive system is made up of internal and external organs that function to produce haploid female gametes called ova, secrete female sex hormones (such as estrogen), and carry and give birth to a .
- Female reproductive system organs include the , , , , , and .
-
- The vagina is an elastic, muscular canal that can accommodate the penis. It is where sperm are usually ejaculated during sexual intercourse. The vagina is also the birth canal, and it channels the flow of menstrual blood from the uterus. A healthy vagina has a balance of and an acidic .
- The uterus is a muscular organ above the vagina where a fetus develops. Its muscular walls contract to push out the fetus during childbirth. The is the neck of the uterus that extends down into the vagina. It contains a canal connecting the vagina and uterus for sperm or an infant to pass through. The innermost layer of the uterus, the , thickens each month in preparation for an embryo but is shed in the following menstrual period if fertilization does not occur.
- The oviducts extend from the uterus to the ovaries. Waving at the ovary ends of the oviducts guide ovulated ova into the tubes where fertilization may occur as the ova travel to the uterus. and peristalsis help eggs move through the tubes. Tubular fluid helps nourish sperm as they swim up the tubes toward eggs.
- The ovaries are gonads that produce eggs and secrete sex hormones including estrogen. Nests of cells called follicles in the ovarian cortex are the functional units of ovaries. Each follicle surrounds an immature ovum. At birth, a baby girl’s ovaries contain at least a million eggs, and they will not produce any more during her lifetime. One egg matures and is typically ovulated each month during a woman’s reproductive years.
- The is a general term for external female reproductive organs. The vulva includes the , two pairs of , and openings for the and vagina. Secretions from Bartholin’s glands near the vaginal opening lubricate the vulva.
- The are technically not reproductive organs, but their produce milk to feed an infant after birth. Milk drains through ducts and sacs and out through the nipple when a baby sucks.
- is the process of producing eggs in the ovaries of a female fetus. Oogenesis begins when a diploid oogonium divides by mitosis to produce a diploid primary . The primary oocyte begins meiosis I and then remains at this stage in an immature ovarian follicle until after birth.
- After puberty, one follicle a month matures and its primary oocyte completes meiosis I to produce a secondary oocyte, which begins meiosis II. During ovulation, the mature follicle bursts open and the secondary oocyte leaves the ovary and enters a oviducts.
- While a follicle is maturing in an ovary each month, the endometrium in the uterus is building up to prepare for an . Around the time of ovulation, cervical mucus becomes thinner and more alkaline to help sperm reach the secondary oocyte.
- If the secondary oocyte is fertilized by a sperm, it quickly completes meiosis II and forms a , which will continue through the oviducts. The zygote will go through multiple cell divisions before reaching and implanting in the uterus. If the secondary oocyte is not fertilized, it will not complete meiosis II, and will soon disintegrate.
- is the carrying of one or more offspring from fertilization until birth. The maternal organism must provide all the nutrients and other substances needed by the developing offspring, and also remove its wastes. She should also avoid exposures that could potentially damage the offspring, especially early in the pregnancy when organ systems are developing.
-
- The average duration of pregnancy is 40 weeks (from the first day of the last menstrual period) and is divided into three trimesters of about three months each. Each trimester is associated with certain events and conditions that a pregnant woman may expect, such as morning sickness during the first trimester, feeling fetal movements for the first time during the second trimester, and rapid weight gain in both fetus and mother during the third trimester.
- , which is the general term for the birth process, usually begins around the time the amniotic sac breaks and its fluid leaks out. Labour occurs in three stages: dilation of the cervix, birth of the baby, and delivery of the placenta (afterbirth).
- The physiological function of female breasts is , or the production of breast milk to feed an infant. Sucking on the breast by the infant stimulates the release of the hypothalamic hormone from the posterior pituitary, which causes the flow of milk. The release of milk stimulates the baby to continue sucking, which in turn keeps the milk flowing. This is one of the few examples of in the human organism.
- The ovaries produce female sex hormones, including estrogen and . Estrogen is responsible for sexual maturation and secondary sex characteristics at puberty. It is also needed to help regulate the menstrual cycle and ovulation after puberty until menopause. Progesterone prepares the uterus for pregnancy each month during the menstrual cycle, and helps maintain the pregnancy if fertilization occurs.
- The menstrual cycle refers to natural changes that occur in the female reproductive system each month during the reproductive years, except when a woman is pregnant. The cycle is necessary for the production of ova and the preparation of the uterus for pregnancy. It involves changes in both the ovaries and uterus and is controlled by pituitary hormones (FSH and LH) and ovarian hormones (estrogen and progesterone).
-
- The female reproductive period is delineated by , or the first menstrual period, which usually occurs around age 12 or 13; and by , or the cessation of menstrual periods, which typically occurs around age 52. A typical menstrual cycle averages 28 days in length but may vary normally from 21 to 45 days. The average menstrual period is five days long, but may vary normally from two to seven days. These variations in the menstrual cycle may occur both between women and within individual women from month to month.
- The events of the menstrual cycle that take place in the ovaries make up the . It includes the , when a follicle and its ovum mature due to rising levels of FSH; ovulation, when the ovum is released from the ovary due to a rise in estrogen and a surge in LH; and the , when the follicle is transformed into a structure called a that secretes progesterone. In a 28-day menstrual cycle, the follicular and luteal phases typically average about two weeks in length, with ovulation generally occurring around day 14 of the cycle.
- The events of the menstrual cycle that take place in the uterus make up the . It includes , which generally occurs on days 1 to 5 of the cycle and involves shedding of endometrial tissue that built up during the preceding cycle; the , during which the endometrium builds up again until ovulation occurs; and the , which follows ovulation and during which the endometrium secretes substances and undergoes other changes that prepare it to receive an .
- Disorders of the female reproductive system include , , and .
-
- Cervical cancer occurs when cells of the cervix grow abnormally and develop the ability to invade nearby tissues, or spread to other parts of the body. Worldwide, cervical cancer is the second-most common type of cancer in females and the fourth-most common cause of cancer death in females. Early on, cervical cancer often has no symptoms; later, symptoms such as abnormal vaginal bleeding and pain are likely.
-
-
- Most cases of cervical cancer occur because of infection with , so the HPV vaccine is expected to greatly reduce the incidence of the disease. Other risk factors include smoking and a weakened immune system. A can diagnose cervical cancer at an early stage. Where Pap smears are done routinely, cervical cancer death rates have fallen dramatically. Treatment of cervical cancer generally includes surgery, which may be followed by radiation therapy or chemotherapy.
- Vaginitis is inflammation of the vagina. A discharge is likely, and there may be itching and pain. About 90% of cases of vaginitis are caused by infection with , typically by the yeast Candida albicans. A minority of cases are caused by irritants or allergens in products such as soaps, spermicides, or douches.
-
-
-
- Diagnosis of vaginitis may be based on characteristics of the discharge, which can be examined microscopically or cultured. Treatment of vaginitis depends on the cause, and is usually an oral or topical anti-fungal or antibiotic medication.
- Endometriosis is a disease in which endometrial tissue grows outside the uterus. This tissue may bleed during the menstrual period and cause inflammation, pain, and scarring. The main symptom of endometriosis is pelvic pain, which may be severe. Endometriosis may also lead to infertility.
-
-
-
- Endometriosis is thought to have multiple causes, including genetic mutations. Retrograde menstruation may be the immediate cause of endometrial tissue escaping the uterus and entering the pelvic cavity. Endometriosis is usually treated with surgery to remove the abnormal tissue and medication for pain. If surgery is more conservative than hysterectomy, endometriosis may recur.
-
- is the inability of a sexually mature adult to reproduce by natural means. It is defined scientifically and medically as the failure to achieve a successful pregnancy after at least one year of regular, unprotected sexual intercourse.
- About 40% of infertility in couples is due to female infertility, and another 30% is due to male infertility. In the remaining cases, a couple’s infertility is due to problems in both partners or to unknown causes.
- Male infertility occurs when there are no or too few healthy, motile sperm. This may be caused by problems with spermatogenesis or by blockage of the male reproductive tract that prevents sperm from being ejaculated. Risk factors for male infertility include heavy alcohol use, smoking, certain medications, and advancing age, to name just a few.
- Female infertility occurs due to failure to produce viable ova by the ovaries or structural problems in the oviducts or uterus. Polycystic ovary syndrome is the most common cause of failure to produce viable eggs. Endometriosis and uterine fibroids are possible causes of structural problems in the oviducts and uterus. Risk factors for female infertility include smoking, stress, poor diet, and older age, among others.
- Diagnosing the cause(s) of a couple’s infertility generally requires testing both the man and the woman for potential problems. For men, semen is likely to be examined for adequate numbers of healthy, motile sperm. For women, signs of ovulation are monitored, for example, with an ovulation test kit or ultrasound of the ovaries. For both partners, the reproductive tract may be medically imaged to look for blockages or other abnormalities.
-
- Treatments for infertility depend on the cause. For example, if a medical problem is interfering with sperm production, medication may resolve the underlying problem so sperm production is restored. Blockages in either the male or the female reproductive tract can often be treated surgically. If there are problems with ovulation, hormonal treatments may stimulate ovulation.
- Some cases of infertility are treated with . This is a collection of medical procedures in which eggs and sperm are taken from the couple and manipulated in a lab to increase the chances of fertilization occurring and an embryo forming. Other approaches for certain causes of infertility include the use of a surrogate mother, gestational carrier, or sperm donation.
- Infertility can negatively impact a couple socially and psychologically, and it may be a major cause of marital friction or even divorce. Infertility treatments may raise ethical issues relating to the costs of the procedures and the status of embryos that are created in vitro but not used for pregnancy. Infertility is an under-appreciated problem in developing countries where birth rates are high and children have high economic as well as social value. In these countries, poor health care is likely to lead to more problems with infertility and fewer options for treatment.
- More than half of all fertile couples worldwide use contraception (birth control), which is any method or device used to prevent pregnancy. Different methods of contraception vary in their effectiveness, typically expressed as the failure rate, or the percentage of women who become pregnant using a given method during the first year of use. For most methods, the failure rate with typical use is much higher than the failure rate with perfect use.
- Types of birth control methods include , hormonal methods, intrauterine devices, behavioural methods, and . Except for sterilization, all of the methods are reversible.
-
- Barrier methods are devices that block sperm from entering the uterus. They include condoms and diaphragms. Of all birth control methods, only condoms can also prevent the spread of sexually transmitted infections.
- Hormonal methods involve the administration of hormones to prevent ovulation. Hormones can be administered in various ways, such as in an injection, through a skin patch, or, most commonly, in birth control pills. There are two types of birth control pills: those that contain estrogen and progesterone, and those that contain only progesterone. Both types are equally effective, but they have different potential side effects.
- An intrauterine device (IUD) is a small T-shaped plastic structure containing copper or a hormone that is inserted into the uterus by a physician and left in place for months or even years. It is highly effective even with typical use, but it does have some risks, such as increased menstrual bleeding and, rarely, perforation of the uterus.
- Behavioural methods involve regulating the timing or method of intercourse to prevent introduction of sperm into the female reproductive tract, either altogether or when an egg may be present. In fertility awareness methods, unprotected intercourse is avoided during the most fertile days of the cycle as estimated by basal body temperature or the characteristics of cervical mucus. In withdrawal, the penis is withdrawn from the vagina before ejaculation occurs. Behavioural methods are the least effective methods of contraception.
- Sterilization is the most effective contraceptive method, but it requires a surgical procedure and may be irreversible. Male sterility is usually achieved with a vasectomy, in which the vas deferens are clamped or cut to prevent sperm from being ejaculated in semen. Female sterility is usually achieved with a tubal ligation, in which the oviducts are clamped or cut to prevent sperm from reaching and fertilizing eggs.
- Emergency contraception is any form of contraception that is used after unprotected vaginal intercourse. One method is the “morning after” pill, which is a high-dose birth control pill that can be taken up to five days after unprotected sex. Another method is an IUD, which can be inserted up to five days after unprotected sex.
In this chapter, you learned how the male and female reproductive systems work together to produce a zygote. In the next chapter, you will learn about how the human organism grows and develops throughout life — from a zygote all the way through old age.
Chapter 18 Review
- Which glands produce the non-sperm fluids that make up semen? What is the rough percentage of each fluid in semen?
- What is one reason why semen's alkalinity assists in reproduction?
- What are three things that pass through the cervical canal of females, going in either direction?
- Other than where the cancer originates, what is one difference between prostate and testicular cancer?
- If a woman is checking her basal body temperature each morning as a form of contraception, and today is day 12 of her menstrual cycle and her basal body temperature is still low, is it safe for her to have unprotected sexual intercourse today? Why or why not?
- Where is a diaphragm placed? How does it work to prevent pregnancy?
- Why are the testes located outside of the body?
- Why is it important to properly diagnose the causative agent when a woman has vaginitis?
- Describe two ways in which sperm can move through the male and/or female reproductive tracts.
Attributions
Figure 18.12.1
Pregnancy test/ Dos rayitas by Esparta Palma on Flickr is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/) license.
Figure 18.12.2
1024px-Ovulatietest by Sapp on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 18.12.3
Sperm Count by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
References
Brainard, J/ CK-12 Foundation. (2016). Figure 3 Normal vs. low sperm count [digital image]. In CK-12 College Human Biology (Section 20.12) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/20.12/
A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.
The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Thus, the amount of matter cannot change.
Created by CK-12 Foundation/Adapted by Christine Miller
Nail Art
Painting nails with coloured polish for aesthetic reasons is nothing new. In fact, there is evidence of this practice dating back to at least 3000 BCE. Today, painting and otherwise decorating the nails is big business, with annual revenues in the billions of dollars in North America alone! With all the attention (and money) given to nails as decorative objects, it’s easy to forget that they also have important biological functions.
What Are Nails?
s are accessory organs of the . They are made of sheets of dead and are found on the far (or distal) ends of the fingers and toes. The keratin in nails makes them hard, but flexible. Nails serve a number of purposes, including protecting the digits, enhancing sensations, and acting as tools.
Nail Anatomy
A nail has three main parts: the root, plate, and free margin. Other structures around or under the nail include the nail bed, cuticle, and nail fold. These structures are shown in Figure 10.6.2.
- The is the portion of the nail found under the surface of the skin at the near (or proximal) end of the nail. It is where the nail begins.
- The (or body) is the portion of the nail that is external to the skin. It is the visible part of the nail.
- The is the portion of the nail that protrudes beyond the distal end of the finger or toe. This is the part that is cut or filed to keep the nail trimmed.
- The is the area of skin under the nail plate. It is pink in colour, due to the presence of capillaries in the dermis.
- The is a layer of dead epithelial cells that overlaps and covers the edge of the nail plate. It helps to seal the edges of the nail to prevent infection of the underlying tissues.
- The is a groove in the skin in which the side edges of the nail plate are embedded.
Nail Growth
Nails grow from a deep layer of living epidermal tissue, known as the , at the proximal end of the nail (see the bottom of the diagram in Figure 10.6.2). The nail matrix surrounds the nail root. It contains stem cells that divide to form keratinocytes, which are cells that produce keratin and make up the nail.
Formation of the Nail Root and Nail Plate
The produced by the nail matrix accumulate to form tough, hard, translucent sheets of dead cells filled with . The sheets make up the nail root, which slowly grows out of the skin and becomes the nail plate when it reaches the skin surface. As the nail grows longer, the cells of the nail root and nail plate are pushed toward the distal end of the finger or toe by new cells being formed in the nail matrix. The upper epidermal cells of the nail bed also move along with the nail plate as it grows toward the tip of the digit.
The proximal end of the nail plate near the root has a whitish crescent shape called the . This is where a small amount of the nail matrix is visible through the nail plate. The lunula is most pronounced in the nails of the thumbs, and may not be visible in the nails of the little fingers.
Rate of Nail Growth
Nails grow at an average rate of 3 mm a month. Fingernails, however, grow up to four times as fast as toenails. If a fingernail is lost, it takes between three and six months to regrow completely, whereas a toenail takes between 12 and 18 months to regrow. The actual rate of growth of an individual’s nails depends on many factors, including age, sex, season, diet, exercise level, and genes. If protected from breaking, nails can sometimes grow to be very long. The Chinese doctor in the photo below (Figure 10.6.3) has very long nails on two fingers of his left hand. This picture was taken in 1920 in China, where having long nails was a sign of aristocracy since it implied that one was wealthy enough to not have to do physical labour.
Functions of Nails
Both fingernails and toenails protect the soft tissues of the fingers and toes from injury. Fingernails also serve to enhance sensation and precise movements of the fingertips through the counter-pressure exerted on the pulp of the fingers by the nails. In addition, fingernails can function as several different types of tools. For example, they enable a fine precision grip like tweezers, and can also be used for cutting and scraping.
Nails and Health
Healthcare providers, particularly EMTs, often examine the fingernail beds as a quick and easy indicator of oxygen saturation of the blood, or the amount of blood reaching the extremities. If the nail beds are bluish or purple, it is generally a sign of low oxygen saturation. To see if blood flow to the extremities is adequate, a blanch test may be done. In this test, a fingernail is briefly depressed to turn the nail bed white by forcing the blood out of its capillaries. When the pressure is released, the pink colour of the nail bed should return within a second or two if there is normal blood flow. If the return to a pink colour is delayed, then it can be an indicator of low blood volume, due to dehydration or shock.
How the visible portion of the nails appears can be used as an indicator of recent health status. In fact, nails have been used as diagnostic tools for hundreds — if not thousands — of years. Nail abnormalities, such as deep grooves, brittleness, discolouration, or unusually thin or thick nails, may indicate various illnesses, nutrient deficiencies, drug reactions, or other health problems.
Nails — especially toenails — are common sites of fungal infections (shown in Figure 10.6.4), causing nails to become thickened and yellowish in colour. Toenails are more often infected than fingernails because they are often confined in shoes, which creates a dark, warm, moist environment where fungi can thrive. Toes also tend to have less blood flow than fingers, making it harder for the immune system to detect and stop infections in toenails.
Although nails are harder and tougher than skin, they are also more permeable. Harmful substances may be absorbed through the nails and cause health problems. Some of the substances that can pass through the nails include the herbicide Paraquat, fungicidal agents such as miconazole (e.g., Monistat), and sodium hypochlorite, which is an ingredient in common household bleach. Care should be taken to protect the nails from such substances when handling or immersing the hands in them by wearing latex or rubber gloves.
Feature: Reliable Sources
Do you get regular manicures or pedicures from a nail technician? If so, there is a chance that you are putting your health at risk. Nail tools that are not properly disinfected between clients may transmit infections from one person to another. Cutting the cuticles with scissors may create breaks in the skin that let infective agents enter the body. Products such as acrylics, adhesives, and UV gels that are applied to the nails may be harmful, especially if they penetrate the nails and enter the skin.
Use the Internet to find several reliable sources that address the health risks of professional manicures or pedicures. Try to find answers to the following questions:
- What training and certification are required for professional nail technicians?
- What licenses and inspections are required for nail salons?
- What hygienic practices should be followed in nail salons to reduce the risk of infections being transmitted to clients?
- Which professional nail products are potentially harmful to the human body and which are safer?
- How likely is it to have an adverse health consequence when you get a professional manicure or pedicure?
- What steps can you take to ensure that a professional manicure or pedicure is safe?
10.6 Summary
- are accessory organs of the , consisting of sheets of dead, keratin-filled . The keratin in nails makes them hard, but flexible.
- A nail has three main parts: the (which is under the epidermis), the (which is the visible part of the nail), and the (which is the distal edge of the nail). Other structures under or around a nail include the , , and .
- A nail grows from a deep layer of living epidermal tissues — called the — at the proximal end of the nail. Stem cells in the nail matrix keep dividing to allow nail growth, forming first the nail root and then the nail plate as the nail continues to grow longer and emerges from the epidermis.
- Fingernails grow faster than toenails. Actual rates of growth depend on many factors, such as age, sex, and season.
- Functions of nails include protecting the digits, enhancing sensations and precise movements of the fingertips, and acting as tools.
- The colour of the nail bed can be used to quickly assess oxygen and blood flow in a patient. How the nail plate grows out can reflect recent health problems, such as illness or nutrient deficiency.
- Nails — and especially toenails — are prone to fungus infections. Nails are more permeable than skin and can absorb several harmful substances, such as herbicides.
10.6 Review Questions
- What are nails?
- Explain why most of the nail plate looks pink.
- Describe a lunula.
- Explain how a nail grows.
- Identify three functions of nails.
- Give several examples of how nails are related to health.
- What is the cuticle of the nail composed of? What is the function of the cuticle? Why is it a bad idea to cut the cuticle during a manicure?
- Is the nail plate composed of living or dead cells?
10.6 Explore More
https://www.youtube.com/watch?v=G35kPhbUZdg
Longest Fingernails - Guinness World Records 60th Anniversary,
Guinness World Records, 2014.
https://www.youtube.com/watch?v=aTSVHwzkYI4&feature=emb_logo
5 Things Your Nails Can Say About Your Health, SciShow, 2015.
https://www.youtube.com/watch?v=7w2gCBL1MCg
Claws vs. Nails - Matthew Borths, TED-Ed, 2019.
Attributions
Figure 10.6.1
Nails by allison-christine-vPrqHSLdF28 [photo] by allison christine on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 10.6.2
Blausen_0406_FingerNailAnatomy by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 10.6.3
Chinese_doctor_with_long_finger_nails_(an_aristocrat),_ca.1920_(CHS-249) by Pierce, C.C. (Charles C.), 1861-1946 from the USC Digital Library on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain).
Figure 10.6.4
Toenail fungus Nagelpilz-3 by Pepsyrock on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/public_domain).
Figure 10.6.5
OLYMPUS DIGITAL CAMERA by Stoive at the English language Wikipedia, on Wikimedia Commons is used under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/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.
Guiness World Records. (2014, December 8). Longest fingernails - Guinness World Records 60th Anniversary. YouTube. https://www.youtube.com/watch?v=G35kPhbUZdg
SciShow. (2015, September 14). 5 things your nails can say about your health. YouTube. https://www.youtube.com/watch?v=aTSVHwzkYI4
TED-Ed. (2019, October 29). Claws vs. nails - Matthew Borths. YouTube. https://www.youtube.com/watch?v=7w2gCBL1MCg
Created by CK-12 Foundation/Adapted by Christine Miller
Bathing in Sunshine
Summer sun may feel good on your body, but its invisible wreak havoc on your skin. Exposing the skin to UV light causes photo-aging: premature wrinkling, brown discolourations, and other unattractive signs of sun exposure. Even worse, UV light increases your risk of skin cancer.
What Is Skin Cancer?
Skin is a disease in which skin cells grow out of control. It is caused mainly by excessive exposure to UV light, which damages . Therefore, skin cancer most often develops on areas of the skin that are frequently exposed to UV light. However, it can also occur on areas that are rarely exposed to UV light. Skin cancer affects people of all skin colours, including those with dark skin. It also affects more people altogether than all other cancers combined. One in five Canadians develops skin cancer in his or her lifetime.
Types of Skin Cancer
Skin cancer begins in the outer layer of skin, the . There are three common types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma.
Basal Cell Carcinoma
occurs in basal cells of the epidermis. Basal cells are in the layer that divide to form all the keratinocytes of the epidermis. Basal cell carcinoma is the most common form of skin cancer and 1 in 8 Canadians will develop basal cell carcinoma during their lifetime. A basal cell carcinoma may appear as a pearly or waxy sore, like the one shown in Figure 10.7.2. Basal cell carcinomas rarely spread (or undergo ), so they can generally be cured with a , in which the lesion is cut out of the skin and analyzed in a medical lab.
Squamous Cell Carcinoma
occurs in squamous cells of the epidermis. Squamous cells are flattened, -filled cells in upper layers of the epidermis. Squamous cell carcinoma is the second most common form of skin cancer. More than two million cases occur in the United States each year. A squamous cell carcinoma may appear as a firm, red nodule, or as a flat lesion with a scaly or crusty surface, like the one pictured in Figure 10.7.3. Squamous cell carcinomas are generally localized and unlikely to metastasize, so they are usually curable surgically.
Melanoma
occurs in of the epidermis. Melanocytes are the melanin-producing cells in the stratum basale of the epidermis. Melanoma is the rarest type of skin cancer, accounting for less than one per cent of all skin cancer cases. Melanoma, however, is the most deadly type of skin cancer. It causes the vast majority of skin cancer deaths, because melanoma is malignant. If not treated, it will metastasize and spread to other parts of the body. If melanoma is detected early and while it is still localized in the skin, most patients survive for at least five years. If melanoma is discovered only after it has already metastasized to distant organs, there is only a 17% of patients surviving for five years. You can see an example of a melanoma in Figure 10.7.4.
Melanoma can develop anywhere on the body. It may develop in otherwise normal skin, or an existing mole may become cancerous. Signs of melanoma may include a:
- Mole that changes in size, feel, or colour.
- Mole that bleeds.
- Large brown spot on the skin sprinkled with darker specks.
- Small lesion with an irregular border and parts that appear red, white, blue, or blue-black.
- Dark lesion on the palms, soles, fingertips, toes, or mucous membranes.
Skin Cancer Risk Factors
Exposure to UV radiation causes about 90 per cent of all skin cancer cases. The connection between skin cancer and UV light is so strong that the World Health Organization has classified UV radiation (whether from tanning beds or the sun) as a Group 1 carcinogen (cancer-causing agent). Group 1 carcinogens are those carcinogens that are known with virtual certainty to cause cancer. In addition to UV light, Group 1 carcinogens include tobacco and plutonium. In terms of numbers of cancers caused, UV radiation is far worse than tobacco. More people develop skin cancer because of UV light exposure than develop lung cancer because of smoking. The increase in cancer risk due to UV light is especially great if you have ever had blistering sunburns as a child or teen.
Besides UV light exposure, other risk factors for skin cancer include:
- Having light coloured skin.
- Having a lot of moles.
- Being diagnosed with precancerous skin lesions.
- Having a family history of skin cancer.
- Having a personal history of skin cancer.
- Having a weakened immune system.
- Being exposed to other forms of radiation or to certain toxic substances such as arsenic.
Feature: My Human Body
As with most types of cancer, skin cancer is easiest to treat and most likely to be cured the earlier it is detected. The skin is one of the few organs that you can monitor for cancer yourself, as long as you know what to look for. A brown spot on the skin is likely to be a harmless mole, but it could be a sign of skin cancer. As shown in Figure 10.7.5 below, unlike moles, skin cancers may be asymmetrical, have irregular borders, may be very dark in colour, and may have a relatively great diameter. These characteristics can be remembered with the acronym ABCD.
With the help of mirrors, you should check all of your skin regularly. Look for new skin growths or changes in any existing moles, freckles, bumps, or birthmarks. Report anything suspicious or different to your doctor.
If you have risk factors for skin cancer, it’s a good idea to have an annual skin check by a dermatologist. This helps ensure that cancerous or precancerous lesions will be detected before they grow too large and become difficult to cure, or in the case of melanoma, before they metastasize.
10.7 Summary
- Skin is a disease in which skin cells grow out of control. It is caused mainly by excessive exposure to , which damages . Skin cancer affects more Canadians than all other cancers combined. There are three common types of skin cancer: , , and . Carcinomas are more common and unlikely to metastasize. Melanoma is rare and likely to metastasize. It causes most skin cancer deaths.
- Besides exposure to UV light, risk factors for skin cancer include having light coloured skin, having lots of moles, and a family history of skin cancer, among several others.
10.7 Review Questions
- What is skin cancer?
- How common is skin cancer?
- Compare and contrast the three common types of skin cancer.
- Identify factors that increase the risk of skin cancer.
- How does exposure to UV light cause skin cancer?
- In which layer of the skin does skin cancer normally start?
- Which two skin cancers described in this section start in the same sub-layer? Include the name of the sub-layer and the cells affected in each of these cancers.
- Which type of skin cancer is most likely to spread to other organs? Explain your answer.
- Which form of skin cancer is the most deadly?
- What are some ways people can reduce their risk of getting skin cancer? Explain your answer.
10.7 Explore More
https://www.youtube.com/watch?v=60e-t4zglBk&feature=emb_logo
The skin 'beauty' and the sun 'beast': Charareh Pourzand at TEDxBathUniveristy, TEDx Talks, 2014.
https://www.youtube.com/watch?v=ID-O-Ion3EQ&feature=emb_logo
Cancer of the Vulva, Robert Miller, 2014.
https://www.youtube.com/watch?v=BmFEoCFDi-w
How do cancer cells behave differently from healthy ones? - George Zaidan, TED-Ed, 2012.
Attributions
Figure 10.7.1
Stolen_Moment_in_the_Sun by Angie Garrett on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 10.7.2
Basal_cell_carcinoma,_ulcerated by Kelly Nelson (Photographer) from National Cancer Institute (part of the National Institutes of Health) with the ID 9237 on Wikimedia Commons was released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 10.7.3
Squamous_cell_carcinoma_(1) by Kelly Nelson (Photographer) from National Cancer Institute (part of the National Institutes of Health) with the ID 9248 on Wikimedia Commons was released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 10.7.4
Melanoma by Unknown author (Photographer) from National Cancer Institute (part of the National Institutes of Health) with the AV-8500-3850/ ID 9186 on Wikimedia Commons was released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 10.7.5
ABCDs of skin cancer by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license. (Original images courtesy of NCI: ID numbers 2362; 2363; 2364; and 2184)
References
Brainard, J/ CK-12 Foundation. (2016). Figure 5 ABCDs of skin cancer[digital image]. In CK-12 College Human Biology (Section 12.7) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/12.7/
Public Health Agency of Canada. (2019, December 9). Non melanoma skin cancer. Canada.ca. https://www.canada.ca/en/public-health/services/chronic-diseases/cancer/non-melanoma-skin-cancer.html
Robert Miller. (2014, July 22). Cancer of the vulva. YouTube. https://www.youtube.com/watch?v=ID-O-Ion3EQ
TED-Ed. (2012, December 5). How do cancer cells behave differently from healthy ones? - George Zaidan. YouTube. https://www.youtube.com/watch?v=BmFEoCFDi-w
TEDx Talks. (2014, March 28). The skin 'beauty' and the sun 'beast': Charareh Pourzand at TEDxBathUniveristy. YouTube. https://www.youtube.com/watch?v=60e-t4zglBk
A double-membrane-bound organelle found in most eukaryotic organisms. Mitochondria convert oxygen and nutrients into adenosine triphosphate (ATP). ATP is the chemical energy "currency" of the cell that powers the cell's metabolic activities.
Respiration using electron acceptors other than molecular oxygen. Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
Image shows a pictomicrograph of the layers of the GI tract. Each of the mucosa, submucosa, muscularis and serosa are differentiated with respect to colouration and cell shape/size.
The central nervous system organ inside the skull that is the control center of the nervous system.