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Disease and Immunity, Wellness and Fitness 14 After you have finished reading this chapter, you should be able to: Compare and contrast the various factors that cause disease. Identify the body’s defenses against disease-causing organisms. Describe the structures and functions of the human immune system. And it is well to superintend the sick to make them well, to care for the healthy to keep them well, also to care for one’s own self, so as to observe what is seemly. Hippocrates, Precepts Introduction In the past, many people believed that evil spirits were the cause of human illness. If someone became ill, the treatment prescribed was often horrific. The patient might be beaten, tortured, or starved. One technique used in some cultures involved drilling a hole in the ill person’s skull to allow the evil spirit to leave. If a sick person didn’t die from the disease, he or she might die from the “cure.” (See Figure 14-1 on page 296.) How different is our understanding of disease today! We have achieved this understanding from the careful thinking, experiments, and observations of many people over a long period of time. Twenty-four hundred years ago, the physician and teacher Hippocrates lived on the small Greek island of Kos. Through his work, Hippocrates did a great deal to move medicine away from superstitions. For this, Hippocrates has been called the “father of medicine.” An article, “Airs, Waters, and Places,” written by Hippocrates—or one of his students—discussed how disease, rather than coming from the gods, may have been related to the weather, drinking water, and winds in the town. The idea that diseases have understandable 295 296 Maintaining a Dynamic Equilibrium Figure 14-1 In an ancient medical procedure, the Incas carved a hole in the patient’s head, attempting to cure an illness. causes was becoming part of medical knowledge. It followed logically that once the causes of diseases were known, sensible treatments could be offered. The need to understand the causes of disease and to discover successful treatments for diseases continues. ■■ DISEASE: A LACK OF HOMEOSTASIS Homeostasis, the theme we have been studying, emphasizes the need for organisms to maintain a carefully controlled internal set of conditions, a dynamic equilibrium. Maintaining these conditions—including pH, temperature, water and salt balance, and levels of CO2 and O2—allows an organism’s cells to function normally. Living organisms allow changes within very definite limits to occur. Changes outside normal limits disrupt homeostasis, producing illness, disease, and possibly even death. There are many reasons why the body can be pushed beyond its normal limits. These reasons, or factors, are often the causes of disease, causes that ancient peoples did not understand. An inherited defect in a genetic trait might be a cause of disease. The disruptions of homeostasis in such a disease would be caused, in a sense, by a factor inside the body. Many other diseases result from some influence outside the body, in the environment. ■■ FACTORS THAT CAUSE DISEASES Diseases may be caused by one of the following factors, or by a combination of several of these factors. ◆ Inheritance. Defective genetic traits can be passed from parents to offspring. Often the parents may not have the disease, but both may carry a single allele (the form of a gene) for the disease. It is the combination of these two defective alleles in the child that gives him or her the disease. Chapter 14 / Disease and Immunity, Wellness and Fitness 297 Figure 14-2 This scanning electron micrograph of red blood cells (magnified more than 7000 times) shows the distorted shape of a cell with flawed hemoglobin. The cause, sickle-cell anemia, is an inherited disease that disrupts homeostasis by obstructing blood flow in capillaries. A well-known example of an inherited disease is sickle-cell anemia. In this condition, hemoglobin, the protein that carries oxygen in red blood cells, is flawed. As a result, the red blood cells may, at times, get twisted out of shape and resemble a sickle, a crescent-shaped tool used to cut grass. (See Figure 14-2.) In the human body, homeostasis is disrupted when the sickle cells obstruct capillaries. The normal movement of blood is interrupted. In addition, the flawed hemoglobin is unable to carry as much oxygen as is normal. At present, sickle-cell anemia cannot be cured. However, problems that arise from the disease are successfully treated. ◆ Microorganisms. Microorganisms that cause disease are called pathogens; they include certain fungi, bacteria, protozoa, and viruses. Some diseases caused by microorganisms may be passed, in a variety of ways, from one person to another. These are called infectious diseases. (See Figure 14-3.) Microorganisms, or microbes, most often enter the body through respiratory pathways, the digestive system, or the urethra. Infections may also occur through breaks in the skin. Some Figure 14-3 Certain microorganisms, such as these rod-shaped bacteria, can cause infectious diseases. 298 Maintaining a Dynamic Equilibrium diseases are more easily transmitted from one person to another than other diseases. Tuberculosis is a disease caused by an infectious microorganism, a rodshaped bacterium. The bacteria that cause tuberculosis travel in the tiny water droplets released into the air when an infected person coughs or sneezes. The bacteria enter the body of another person through the nose or mouth. Once inside the body, the tuberculosis bacteria can infect any tissue, but most often they infect the tissues of the lungs. A person may carry the bacteria in his or her body and not show symptoms of the disease. However, tests can determine if a person has been exposed to the bacteria that cause tuberculosis, even if the person shows no symptoms of this disease. A person with a positive test for the tuberculosis bacteria, or a person who has the disease, is treated with antibiotics. Along with antibiotics, rest and time are necessary for a recovery. However, the problem of antibiotic resistance (discussed in Chapter 1) applies to tuberculosis, too. Some types of tuberculosis have developed that are resistant to the usual course of antibiotics. As a result, new drugs must be produced all the time. ◆ Pollutants and poisons. Chemical agents present in the environment may upset the body’s normal functioning and produce disease. These pollutants include coal dust, asbestos, lead, phosphorus, mercury, polychlorinated biphenyls (PCBs), and many others. For example, when asbestos fibers enter the respiratory system, they cause asbestosis, a disease of the lungs. Years later, cancer in the lungs and chest may result from the inhalation of asbestos fibers. Poisons such as the chemical element arsenic and the toxin from the bacterium Clostridium botulinum are extremely toxic. They quickly cause death. Amazingly, however, both—in very tiny doses or in different forms—are now being used to treat and cure many diseases and ailments. Botox is helping with some 40 ailments, such as cerebral palsy and Parkinson’s, as well as troubles like migraines, excessive sweating, and facial wrinkles. ◆ Organ malfunction. A disease may develop when one or more of the body’s organs malfunction. When an organ such as the liver, lung, heart, stomach, or kidney does not function properly, serious effects on the body result. As you saw in Chapter 13, problems in the nephrons of the kidneys may lead to kidney failure. This causes the disease uremia. Waste products that should have been removed by the kidneys begin to build up in the blood. Chapter 14 / Disease and Immunity, Wellness and Fitness 299 Figure 14-4 Dialysis machines can take the place of kidneys, but only temporarily. Today, technology offers hope to people with kidney failure. Dialysis, featured in Chapter 13, is a process in which a person’s blood is pumped LIVING ENVIRONMENT 14-4 s/s removing the wastes from the through an artificial BIOLOGY, kidney to2e/fig. be cleansed, blood. (See Figure 14-4.) But dialysis provides only temporary help. Kidney transplant operations offer a more permanent treatment. ◆ Harmful lifestyles. The way one lives can also be an important factor in causing disease. Specifically, tobacco, alcohol, and drugs in the body can disrupt homeostasis, producing illness. In addition, overeating, not exercising, having unsafe sexual experiences, and living with stress can lead to certain diseases. Hypertension, or high blood pressure, is one such disease. Hypertension involves an increased pressure on the walls of arteries. Untreated, hypertension can lead to heart attacks, strokes, and damage to the kidneys, nervous system, and eyes. While medications are used to treat severe hypertension, a less stressful lifestyle combined with a diet that is low in sodium may help lower a person’s blood pressure. Moderate exercise, on the advice of a physician, is also an important treatment for hypertension. ■■ THE BODY’S DEFENSES AGAINST DISEASE Our bodies are surrounded by microorganisms trying to get into us. Some of them succeed, through the nose, through cuts in our skin, or along with the food we eat. Many of these microorganisms cause serious problems if they survive and reproduce inside us without challenge. Controlling these 300 Maintaining a Dynamic Equilibrium microscopic invaders is as important to homeostasis as is regulating body temperature and chemistry. The methods by which the body keeps out, or deals with, invading microorganisms are called lines of defense. The lines of defense can be either nonspecific or specific. A nonspecific line of defense keeps out any microorganism. It does not matter what particular invading microorganism it is. A specific line of defense attacks only a particular microorganism, one type at a time. The first line of defense against infection is nonspecific. It consists of physical barriers that block the entry of microorganisms. The skin is the main physical barrier in our body. Because it is made up of a continuous layer of flat, tough cells, it protects the body from invaders as long as it is undamaged. Fluids are also released at certain places on the body to keep out microorganisms. For example, mucus in the passages of the respiratory system, saliva in the mouth, and tears around the eyes all contain substances that kill microorganisms. The strong acid in the stomach is very effective in killing microorganisms in the food we eat. A second line of defense is present when microorganisms get through our physical barriers. We have all experienced a cut or scrape on the skin. In time, the injured area becomes warm, reddened, and perhaps swollen with pus. What is happening? The events described are called inflammation. (See Figure 14-5.) When the injury occurs, chemicals are released by the damaged tissues. In the body, these chemicals act like an alarm. They cause an increase in the blood flow to the site of the injury. Responding to the alarm, special white blood cells that can attack invaders arrive. Warm, reddened swollen area of inflammation Bacteria Splinter Epidermis White blood cells phagocytizing bacteria Bacteria Dermis Blood vessels A White blood cells migrating through vessel walls B Figure 14-5 Inflammation is the body’s second line of defense against disease. Chapter 14 / Disease and Immunity, Wellness and Fitness 301 Figure 14-6 During inflammation, phagocytes engulf and destroy microorganisms, which prevents more serious infection. Bacterium Phagocyte These cells are phagocytic. Like an ameba, phagocytes surround and engulf microorganisms, destroying them by ingesting them. All of this LIVING ENVIRONMENT BIOLOGY, 2e/fig. 14-6 s/s activity helps to prevent a more serious infection from developing. The redness, warmth, and pus are signs that the body is healing itself. (See Figure 14-6.) Vertebrates have evolved a very important system that attacks specific invaders. This is the immune system. The immune system knows who the “bad guys” are. The immune system goes after very specific invaders to try to keep them from disrupting normal body functions. ■■ THE IMMUNE SYSTEM An English physician, Edward Jenner, attempted a very famous and very risky experiment in 1796. (If he were alive today, Jenner probably would have been prevented from carrying out this kind of research.) Jenner noticed that people who worked with cows did not usually contract the deadly disease smallpox. He therefore intentionally infected an eight-yearold boy with cowpox, a mild disease similar to smallpox. Jenner suspected that cowpox in some way protected people from catching smallpox. His 302 Maintaining a Dynamic Equilibrium Antibiotics, Infections, and You Antibiotics are used to treat infections in people and animals. Due to the enormous success of antibiotics, their use is very common worldwide. When we are ill, we have come to expect quick, effective treatment with antibiotics. Physicians often prescribe antibiotics at the earliest sign of an infection. One result of the widespread use of these important medicines is a growing number of antibiotic-resistant strains of bacteria. Some scientists have suggested the alarming possibility of infections that will not be treatable by the antibiotics we have. Already, one disease, tuberculosis—which was largely under control—has reappeared in a strain that is much more difficult to treat with antibiotics. Recently, scientists became alarmed when they found—in food being given to chickens—bacteria that are resistant to the most powerful antibiotics. Even though those particular bacteria were harmless, the finding raised the disturbing possibility that these bacteria could pass on their antibiotic resistance to disease-causing bacteria in chickens and, ultimately, in humans. One possible reason that such drug-resistant bacteria are being found more frequently is the heavy use of antibiotics to promote health and growth in farm animals. This is an issue for everyone to be aware of and concerned about. Science has provided us with a group of wonder drugs to treat diseases that once killed many people. However, we must be thoughtful and wise in the use of antibiotics. The laws of nature—in this case, the process of natural selection that produces resistance to antibiotics—can never be ignored. observation that people who worked with cows often came down with cowpox, but rarely if ever contracted smallpox, formed the basis of his hypothesis. After the boy recovered from cowpox, Jenner deliberately injected the boy with smallpox. The boy did not get sick! Did cowpox protect the boy from smallpox? How could a previous illness protect a person from getting sick again? We now know that the immune system defends our bodies against very specific invaders. Each invader—usually a bacterium or virus—has specific protein molecules attached to its surface. Each such molecule is called an antigen. It is these molecules that are detected by the body’s immune system. When the immune system detects an antigen, it produces antibodies —the molecules that an individual produces as a defense against disease. Antibodies provide this defense by binding to the antigens. Once this Chapter 14 / Disease and Immunity, Wellness and Fitness 303 occurs, the invader can be destroyed by the body. As it turns out, the cowpox and smallpox antigens are almost identical. After he was injected with cowpox, the boy’s immune system made antibodies against the cowpox antigen. Later, when he was injected with smallpox, the boy’s body was ready with a defense. The smallpox virus was destroyed with the help of the antibodies that the boy had made against cowpox antigens. That is why he did not get sick. (See Figure 14-7.) Antibody A Antibody B Antigen-binding sites Antigen Antibody C Figure 14-7 Antibodies, part of the immune system, bind to antigens—specific protein molecules on an invader’s surface. This technique came to be known as vaccination. Vacca is the Latin against a number of diseases. People are now given harmless antigens in a vaccine, which cause the body to produce antibodies. LIVING BIOLOGY, 2e/fig. 14-7 s/s word forENVIRONMENT “cow.” Today, vaccines offer protection Check Your Understanding How is the immune system more “specific” in its defense against infection than the defenses presented by the skin and by inflammation reactions? ■■ B CELLS AND T CELLS The immune system also includes B cells and T cells, actually two types of macrophages. These macrophages are kinds of white blood cells that are produced in bone marrow, the thymus gland, the spleen, the lymph nodes, and the tonsils. (See Figure 14-8 on page 304.) Macrophages are the cells (phagocytes) we have already mentioned, which move to infected areas to engulf and digest invading microorganisms. B cells are the ones that respond to specific antigens by beginning to produce antibody proteins that will bind only with that antigen. As time goes on, the body contains many different types of B cells, each producing antibodies for one specific antigen. After having been invaded once by an antigen, some special B cells that recognize that antigen remain 304 Maintaining a Dynamic Equilibrium Tonsil Thymus gland Lymph nodes Spleen Bone marrow Figure 14-8 Macrophages are produced in bone marrow, the thymus gland, the spleen, the lymph nodes, and the tonsils. in the body for the rest of your life. These are called memory B cells. Because they are already present in the body, you instantly start making LIVING ENVIRONMENT BIOLOGY, 2e/fig. 14-8 s/s antibodies the moment you encounter the same invading microorganisms again. That is why individuals usually do not get measles or chicken pox a second time. The immune system remembers the first exposure to the disease and is ready! This type of protection is called active immunity. (See Figure 14-9.) Passive immunity is related to active immunity. In passive immunity, a person is injected with a large quantity of the correct already formed antibodies to a particular antigen. These antibodies protect the body from a disease only for as long as the antibodies remain in the body. However, the body is passive, uninvolved in this protection. It did not make the antibodies and, more important, does not “remember” how to make them. You therefore have protection for a limited time from passive immunity. Antibodies are good at recognizing antigens on invaders only when the invaders are in the fluids in your body but not inside your cells. The problem is that many bacteria and all viruses quickly get inside body cells. Once inside your cells, bacteria and viruses begin to multiply, to really make you sick. To make matters worse, the antibodies cannot find the Chapter 14 / Disease and Immunity, Wellness and Fitness 305 B Cell Populations [Model Types] 1. Antibodies B B B B B B B B B B 2. Assorted Antigens 3. AntigenAntibody complexes Figure 14-9 In active immunity, memory B cells in the body from a previous exposure can instantly make antibodies when they encounter the same antigen. LIVING ENVIRONMENT BIOLOGY, 2e/fig. 14-9 s/s invaders once they are inside cells. It is for this reason that the immune system has T cells. One type of T cell is called cytotoxic, or killer, T cells. Through protein receptors on their surface, they can recognize cells in the body that have been infected with invading microorganisms. This recognition occurs when an antigen present on the surface of an infected cell binds specifically with a receptor protein projecting from the cell membrane of a T cell. Then the killer T cells punch holes in the membranes of the infected cells, sometimes injecting poison into them. The infected cells are killed and the invaders in these cells are destroyed. (See Figure 14-10.) In addition, another important type of T cell acts as a helper. Helper T cells assist both B cells and killer T cells. Without helper T cells, the other members of the immune system family cannot do their job. Just Figure 14-10 Killer T cells can recognize cells in the body that have been infected by invading microorganisms. 306 Maintaining a Dynamic Equilibrium Bone marrow Circulation in blood Immature lymphocytes Thymus B cell migrates into the bloodstream Lymph nodes, spleen, other lymphold tissues and loose connective tissues T cell migrates into the bloodstream Mature B and T cells Mature B and T cells recirculate in blood and lymph Figure 14-11 Mature B and T cells are white blood cells that circulate through the body to fight infection. LIVING ENVIRONMENT BIOLOGY, 2e/fig. 14-11 s/s (rev. 10/13/03) how important helper T cells are is shown by the fact that they are the cells destroyed by the human immunodeficiency virus (HIV), which results in the disease called AIDS. (See Figure 14-11.) ■■ WHEN THINGS GO WRONG: DISEASES OF THE IMMUNE SYSTEM The immune system helps maintain the internal dynamic equilibrium necessary for life. However, the immune system can become out of balance. It can be overactive or underactive, and in either case the body’s equilibrium is upset. Allergic reactions result from overactivity of the immune system. The body responds inappropriately to common substances such as dust, mold, pollen, or certain foods. The immune system begins making a special type of antibody to these substances, which under normal conditions would not stimulate the immune system. These antibodies cause cells in the body to release substances, including histamines, which cause many allergic symptoms, such as extra fluid in the nasal pathways, difficulty breathing, or inflammation (hives). Allergies are often treated with antihistamines, drugs that stop the release of histamine. Some severe allergic Chapter 14 / Disease and Immunity, Wellness and Fitness 307 reactions may be life threatening. These reactions may need other types of medications. Allergies should be treated by a physician. Sometimes the immune system begins to attack normal body tissues. These are called autoimmune diseases and are very serious. Autoimmune diseases include myasthenia gravis, rheumatic fever, lupus erythematosus, and rheumatoid arthritis. (See Figure 14-12.) In all autoimmune diseases, the body is literally rejecting its own tissues. A similar kind of rejection also often occurs when an organ is transplanted from one person to another. Medications that keep the organ recipient’s immune system from attacking and rejecting the newly transplanted organ must be taken. Figure 14-12 These hands have joints that are affected by rheumatoid arthritis, an autoimmune disease. Recent studies seem to indicate that the process of inflammation, which protects us when we are young, may actually contribute to crippling diseases when we get older. For example, only three out of ten heart attacks occur in people whose arteries have narrowed. Researchers now suspect that many heart attacks are caused when a rupture develops in the wall of an artery—brought on by overactive immune system cells causing an inflammation. Sudden clotting occurs, the artery gets blocked, and a heart attack or a stroke may occur. Disease also occurs when the immune system is underactive instead of overactive. These are called immunodeficiency diseases. AIDS, acquired immunodeficiency syndrome, is an immunodeficiency disease. AIDS is caused by a virus that can be transmitted from one person to another. (This disease is not inherited; that is why it is called “acquired.”) AIDS develops when the human immunodeficiency virus, HIV, destroys a person’s helper T cells. The body is no longer able to protect itself from diseases that may attack it. On rare occasions, an individual is born without a functioning immune system. Such children have SCIDS, severe combined immunodeficiency syndrome, and they have almost no defense against diseases. 308 Maintaining a Dynamic Equilibrium Sadly, life expectancy is short for such persons, but progress is being made. Early detection of this condition, followed by bone marrow transplants, has resulted in significant improvements in some children. Drugs that are used to kill cancer cells in the body can also interfere with the immune system. This is called depressed immunity and can cause complications in the treatment of cancer. ■■ DISEASES AND CHOICES: REDUCING RISKS Certain automatic behaviors, such as simple reflexes, reduce the risk of infection. An eye’s blink is a reflex action that protects the eye from particles or objects that could harm it. Conscious thoughts and actions can reduce the risks of contracting certain diseases. Some of the choices we make can have important influences on our health. Factors that cause diseases may be controllable or uncontrollable. When you think about reducing the risk of disease, it is necessary to think about what risks are under your conscious control. For example, if there is an inherited tendency in one’s family to develop lung cancer, this cannot be controlled. On the other hand, risk factors can also influence the development of lung cancer. Smoking cigarettes has been identified as a risk factor that can cause lung cancer. Smoking or not smoking is a choice people make; thus, it can be controlled. The damaging effects of cigarette smoking include a much higher risk of developing not only lung cancer but also heart disease and the painful, fatal disease emphysema. What a person needs to ask is: With what is known about the risks of cigarette smoking, do the risks outweigh the benefits of the activity? Should I begin to smoke? Should I continue to smoke? Reducing risks can also include avoiding exposure to sources of infectious microorganisms. These sources may include polluted water, contaminated food, animals, or people with contagious diseases. However, it is necessary to be informed about the risks. For example, breathing air in the same room as a person with tuberculosis over a long period of time may result in your being infected. On the other hand, sharing a room with a person infected with HIV, even shaking hands, will not make you become infected. However, contact of your body fluids with his or her body fluids, by your blood mixing with his or her blood, sharing a needle, or having sexual intercourse, may certainly cause you to become infected. Reducing the risk of contracting a particular disease is often a matter of behavior and choices. Chapter 14 / Disease and Immunity, Wellness and Fitness 309 ■■ WELLNESS AND FITNESS What is wellness? Wellness is defined as a lifestyle, that is, how one lives. How one lives is a result of many factors. Some factors are outside of one’s control. The inherited characteristics that a person has from birth are one such factor. Other factors are within one’s control. It is mostly these controllable factors that determine how you live. Wellness involves all the various components that make up one’s life. These components are called dimensions. The dimensions of wellness include: ◆ emotional wellness—maintaining good mental health, a positive attitude, high self-esteem, and a strong self-image ◆ physical wellness—maintaining good nutrition, getting regular exercise, and getting adequate sleep ◆ social wellness—having positive interactions with and enjoying being with others ◆ intellectual wellness—having a sense of curiosity and a strong desire to learn ◆ environmental wellness—maintaining a way of life that protects the environment and minimizes harm to one’s surroundings ◆ cultural wellness—being aware of one’s own cultural background while respecting the diversity and richness of the cultures of others ◆ spiritual wellness—paying attention to personal values and beliefs What is fitness? Fitness is more specifically about one’s own body. Fitness has been defined as the ability to carry out normal activities while having enough energy and strength left over to meet an unusual challenge. A fit person can walk to work and then climb eight flights of stairs to the office without suffering physical discomfort. A person who is not fit runs out of breath very early in the climb up the stairs. (See Figure 14-13 on page 310.) How does the body of a fit person differ from the body of a person who is not fit? Remember that for the body to function, it always needs matter and energy. To be fit, there must be an optimum relationship among the different tissues in the body for matter and energy to be used most efficiently. One way of comparing tissues is to look at the ratio of muscle (matter) to fat (stored energy). The amount of fat in one’s body is not as important as the percentage of fat and the amount of muscle. Too little fat limits one’s energy; too much fat can cause many life-threatening Figure 14-13 Fitness is the ability to perform normal activities yet have enough energy and strength to meet an unusual challenge. conditions, such as heart disease. The ideal body fat percentage for men ranges from 15 percent to 18 percent and for women from 20 percent to 22 percent. How does a person develop physical wellness and physical fitness? Eating properly is most important. A person’s daily diet should include the proper amount of carbohydrates, fats, proteins, vitamins, minerals, and water (see Chapter 8). An individual requires a certain number of calories in the diet. For example, the average teenage boy needs about 3000 calories and the average teenage girl needs about 2000 calories per day. The number of calories a person needs is also affected by his or her body size, age, general level of activity, and physical health. For physical wellness and fitness, it is also very important to exercise regularly. Exercise includes aerobic activities, which concentrate on the respiratory and circulatory systems, and strength-training activities, which improve one’s muscles and skeletal system. A combination of both kinds of activities should be a normal and regular part of one’s lifestyle. Finally, adequate rest is essential to good health. Being well rested helps a person feel less stress during the day. The reduction of stress is one of the most important ways of promoting wellness. LABORATORY INVESTIGATION 14 How Does an Earthworm Respond to a Change in Temperature? INTRODUCTION In order to stay healthy, and thus alive, all organisms must maintain relatively constant internal conditions, even when the environment around them changes. In this investigation, you will study the circulatory system of an earthworm as it experiences changes in the temperature of its environment. It is easy to observe the rate of blood flow in an earthworm by studying the pulsing of the dorsal blood vessel, which can be seen through the earthworm’s skin. MATERIALS Paper towels, rectangular pan, live earthworm, clock or watch with second hand, tap water, laboratory thermometer, ice, warm-water bath PROCEDURE 1. Place an earthworm on a paper towel lining the inside of the pan. 2. Find the dorsal blood vessel, located in the middle of the worm’s dorsal surface. Observe the pulsing of the blood vessel. Count the number of beats in one minute. 3. Propose a hypothesis that explains the relationship of the pulse rate of the dorsal blood vessel to the temperature of the worm’s environment. 4. Expose the worm to at least five different temperatures, from nearly freezing to warm. Keep the temperature below 45°C, however. For each temperature, mix hot and cold water, then pour a few centimeters of water into the pan. It is not important to mix the water to an exact temperature. 5. Let the worm adjust to the new temperature for at least three minutes. Then take the temperature of the water and count the number of times the earthworm’s dorsal blood vessel pulses in one minute. Pour off the water and let the earthworm breathe for at least three minutes. 6. Repeat with water of a different temperature. After collecting your data, let the worm rest again. Chapter 14 / Disease and Immunity, Wellness and Fitness 311 7. Plot the data on a graph, with the independent variable (the temperature) on the x-axis and the dependent variable (pulses) on the y-axis. You may also enter data from other students and you should share your data with them. Study the graph for a pattern and, if possible, draw a best-fit curve for the data points. INTERPRETIVE QUESTIONS 1. Why was it necessary to wait for several minutes each time before you took another pulse rate? 2. Why was it necessary to pour off the water to let the worm breathe? 3. Describe any relationship you see in the data on the maintenance of body temperature in the earthworm. 4. What are some possible sources of error in this investigation? 5. Did your data support your hypothesis? 312 Maintaining a Dynamic Equilibrium Chapter 14 / Disease and Immunity, Wellness and Fitness 313 ■■ CHAPTER 14 REVIEW Answer these questions on a separate sheet of paper. VOCABULARY The following list contains all of the boldfaced terms in this chapter. Define each of these terms in your own words. active immunity, allergic reactions, antibodies, antigen, antihistamines, autoimmune diseases, cytotoxic (killer) T cells, dialysis, fitness, histamines, hypertension, immune system, immunodeficiency diseases, infectious diseases, inflammation, macrophages, passive immunity, pathogens, vaccination, wellness PART A—MULTIPLE CHOICE Choose the response that best completes the sentence. 1. Diseases that are contagious, or “catching,” are said to be a. infectious b. hereditary c. viral d. nonspecific. 2. Fitness includes a. being aware of your cultural heritage b. interacting positively with other people c. the ability to carry out normal activities and to meet unusual challenges d. having a healthy lifestyle. 3. Passive immunity a. occurs after a person has had a disease b. wears off after a period of time c. is induced by injecting antigens into the body d. involves the response of memory B cells. 4. An example of an inherited disease is a. tuberculosis b. AIDS c. chicken pox d. sickle-cell anemia. 5. Phagocytes help to protect the body by a. forming a tough physical barrier b. containing acids that kill microorganisms c. eating invading microorganisms d. producing antigens that bind to disease-causing microorganisms. 6. Diseases can be prevented by a. performing the correct religious ceremonies b. keeping windows tightly shut at night c. reducing exposure to harmful chemicals d. scaring the diseases out of sick people, so the diseases do not spread. 7. Dialysis is used to treat a. sickle-cell anemia b. uremia c. antibiotic-resistant tuberculosis d. severe combined immune deficiency syndrome. 8. Hypertension is often associated with a. a high-sodium diet b. asbestos c. inflammation d. histamines. 314 Maintaining a Dynamic Equilibrium 9. Thrush, a yeast infection of the mouth, is rarely seen except in infants, people with AIDS, and people who have received organ transplants. Thrush is thus a sign of a. autoimmunity b. allergies c. inherited disorders d. immune deficiency. 10. Histamines a. provide passive immunity b. cause allergic symptoms c. bind to antigens on microorganisms d. cause autoimmune responses. 11. B cells a. manufacture antibodies b. recognize cells that have been infected by invading microorganisms c. stimulate other macrophages to fight infection d. provide passive immunity. 12. Smoking increases your risk of developing a. cancer b. emphysema c. heart disease d. all of these. 13. Edward Jenner contributed to medical science by a. showing that diseases were caused by natural rather than supernatural forces b. developing a vaccine against smallpox c. discovering killer T cells d. demonstrating that juvenile diabetes is an autoimmune disease. 14. AIDS can be transmitted by a. sneezing b. shaking hands c. unprotected sexual intercourse d. all of these. 15. Because the antigens on strep bacteria are similar to those on human tissues, an untreated strep infection may result in the production of antibodies that attack the heart valves. This is an example of a. an immunodeficiency disease b. a severe allergic reaction c. a disease-promoting lifestyle d. an autoimmune disease. PART B—CONSTRUCTED RESPONSE Use the information in the chapter to respond to these items. 16. On a separate sheet of paper, complete the following table. What is described in the table? DIMENSION DESCRIPTION Being aware of your own cultural background and respecting the culture of others Environmental Interacting positively with others Emotional Spiritual Obtaining good nutrition, regular exercise, and adequate sleep Intellectual Chapter 14 / Disease and Immunity, Wellness and Fitness 315 17. Select three dimensions from the table and describe how you can improve them in your own life. 18. List three nonspecific defenses of the body and explain how each protects against disease. 19. Relate disease to homeostasis. 20. How does a vaccine prevent disease? PART C—READING COMPREHENSION Base your answers to questions 21 through 23 on the information below and on your knowledge of biology. Source: Science News (February 1, 2003): vol. 163, p. 78. As Population Ages, Flu Takes Deadly Turn The annual toll of influenza has risen dramatically since the late 1970s, according to an analysis of U.S. death statistics. One major factor is the advancing average age of the population. Another is the increasing prevalence of virulent strains of the flu virus. Influenza is typically not a direct cause of death, but researchers at the Centers for Disease Control and Prevention in Atlanta, estimated the disease’s contribution to mortality by noting seasonal fluctuations in deaths that might have resulted from underlying flu infections. Bacterial pneumonia, for example, can be a fatal consequence of severe flu. Such calculations suggest that influenza claimed more than 68,000 lives on average during each of the last three flu seasons of the 1990s, William W. Thompson and his colleagues report in the Jan. 8 Journal of the American Medical Association (JAMA). That’s well up from about 16,000 annual deaths attributable to flu during a similar period 2 decades earlier. People over age 65 are nearly 100 times as likely to die from flu than people 5 to 50 years old are, and the efficacy of flu vaccinations wanes in older adults. Responding to the new findings in the same issue of JAMA, David M. Morens of the National Institutes of Health in Bethesda, Md., urges physicians to get annual flu shots, in order to avoid transmitting the virus to patients. They should also encourage their patients, especially older ones, to get the shots, he says. “Even an imperfect vaccine, used optimally, can prevent many thousands of deaths,” says Morens. 21. State two explanations for the increasing number of deaths from influenza in the United States. 22. Explain the connection between bacterial pneumonia and the flu. 23. Describe the actions that doctors are being advised to take to help limit the number of deaths from the flu.