Immune System. Before You Read. Read to Learn

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1 37 Immune System section 1 Infectious Diseases Before You Read Think of a disease that you have had. On the lines below, write the name of the disease and answer the following questions. Is the disease contagious? How is it spread? What causes the disease? Is there a cure? These are the types of questions that scientists ask about diseases. Pathogens are spread by people, other animals, and objects. What You ll Learn how to construct a flow chart of Koch s postulates how diseases are transmitted and the role of reservoirs in the spread of disease the symptoms of bacterial infectious disease Read to Learn Pathogens Cause Infectious Disease An infectious disease is a disease caused when a pathogen is passed from one organism to another, disrupting homeostasis. Colds and athlete s foot are examples of infectious diseases. Pathogens (PA thuh junz) are the cause of infectious diseases. Some, but not all, types of bacteria, viruses, protozoans, fungi, and parasites are members of this group. Not all members of these groups are harmful. Some types of bacteria and protozoans normally live inside your body and on your skin. These organisms help protect your body from pathogens. Germ Theory and Koch s Experiments With the invention of the microscope, scientists discovered microorganisms. Louis Pasteur showed that microorganisms from the air could grow in nutrient solutions. With knowledge gained from discoveries like these, scientists began to develop the germ theory. The germ theory states that some microorganisms are pathogens. Scientists were not able to prove this theory until Robert Koch, a German physician, performed experiments on anthrax (AN thraks). Create a Quiz After you read this section, create a fivequestion quiz from what you have learned. Exchange quizzes with another student. After taking the quizzes, review your answers together. 1. Explain What does the germ theory state? Reading Essentials Chapter 37 Immune System 433

2 How was the first pathogen identified? Robert Koch studied anthrax, a deadly disease that affects cattle and sheep and can also affect people. Koch isolated the anthrax bacterium from the blood of cattle that had died from the disease. After growing the bacterium in a laboratory, Koch injected it into healthy cattle. These cattle developed the disease anthrax. Koch then isolated the anthrax bacterium from the blood of the newly infected cattle and grew it in a laboratory. Koch compared the characteristics of the two sets of cultures. They were identical. This showed that the same type of bacterium caused the illness in both sets of cattle. What are the steps in Koch s postulates? Koch s experimental steps became known as Koch s postulates. Koch s postulates are rules for showing that an organism causes a disease. The figure below lists and illustrates these rules. Scientists still follow Koch s postulates to identify a specific pathogen as the cause of a specific disease. Artificial media are gels containing nutrients that the bacteria need to live and reproduce. Scientists use artificial media to grow bacteria in the laboratory. Some pathogens, including viruses, will not grow on artificial media. Scientists need cultured cells to grow viruses. Picture This 2. Sequence On the line below, write the letters of the following items in the correct sequence. a. pathogen injected into healthy animal causes the disease b. pathogen from second animal shows same characteristics as the first c. pathogen grown in laboratory d. pathogen isolated from animal with the disease 434 Chapter 37 Immune System Reading Essentials

3 Spread of Disease Of the many microorganisms that surround us, only a few cause disease. The table below lists some common human infectious diseases. To spread, a pathogen needs a reservoir and a way to spread. A disease reservoir is a source of the pathogen in the environment. Reservoirs might be animals, people, or objects such as soil or a dirty countertop. How do humans act as reservoirs of pathogens? Humans are the main reservoir for pathogens that infect humans. People can pass pathogens directly or indirectly to other people. Individuals can be capable of passing a pathogen, even if they have no symptoms of the disease. These people are called carriers. Humans can spread colds, influenza (flu), and sexually transmitted diseases, such as human immunodeficiency (ih MYEWN nuh dih fih shun see) virus (HIV), without knowing they are infected. Can other animals pass pathogens to humans? Other animals can also carry pathogens, such as influenza and rabies, that can infect humans. Pigs and birds can spread influenza pathogens. Rabies can pass to humans from dogs and wild animals such as bats, foxes, and skunks. 3. Evaluate Why can keeping a countertop clean help prevent the spread of disease? Picture This 4. Draw Conclusions Use of insect repellent can help protect you from which disease? (Circle your answer.) a. tetanus b. athlete s foot c. West Nile virus Human Infectious Diseases Disease Cause Affected Organ System How Disease is Spread Tetanus bacteria nervous system soil in deep puncture wound Strep throat bacteria respiratory system droplets/direct contact Meningitis bacteria or virus nervous system droplets/direct contact Lyme disease bacteria skeletal and nervous system vector (tick) Chicken pox virus skin droplets/direct contact Rabies virus nervous system animal bite Colds virus respiratory system droplets/direct contact Influenza virus respiratory system droplets/direct contact Hepatitis B virus liver direct contact with exchange of body fluids West Nile virus nervous system vector (mosquito) Giardia protozoan digestive tract contaminated water Malaria protozoan blood and liver vector (mosquito) Reading Essentials Chapter 37 Immune System 435

4 What are some other reservoirs? Some bacteria normally found in soil, such as tetanus, can cause disease in people. Infection can result if the contaminated soil gets into a deep wound. Contaminated water and food are reservoirs of pathogens. Sewage treatment plants prevent human feces from contaminating the water supply. Food can become contaminated through contact with humans or insects. What are the main methods of transmission? Pathogens are mainly transmitted to humans in four ways: (1) direct contact, (2) indirectly through the air, (3) indirectly through touching contaminated objects, and (4) by vectors, organisms that carry pathogens. Direct Contact Direct contact with other humans can spread diseases such as colds, herpes (HUR peez), infectious mononucleosis (mah noh new klee OH sus) (also known as mono or the kissing disease ), and sexually transmitted diseases. 5. Explain how mono is spread. 6. Define toxins. Indirect Contact Some pathogens can be passed through the air. When an infected person sneezes or coughs, pathogens can pass to another person or to an object in tiny mucous droplets. Many pathogens can survive on objects touched by humans. Careful hand washing and cleaning of cooking surfaces and utensils can help prevent the spread of pathogens. Vectors The most common vectors are arthropods, which include biting insects such as mosquitoes and ticks. Flies can pick up pathogens by landing on infected material, such as feces. Flies then spread the pathogens by landing on materials handled or eaten by humans. Symptoms of Disease Symptoms such as aches, coughing, and sneezing result when a pathogen invades cells in your body. Recall from Chapter 18, as the virus multiplies, it damages tissues and kills some cells. Bacteria that invade the body sometimes produce harmful chemicals or toxins. The toxins travel in the bloodstream and can cause damage in different parts of the body. All viruses and some types of bacteria and protozoans invade and live inside cells. They damage and sometimes kill the cells, causing symptoms in the host. 436 Chapter 37 Immune System Reading Essentials

5 Disease Patterns Health agencies constantly observe disease patterns to help control the spread of disease. The Centers for Disease Control and Prevention (CDC) receives information from doctors and clinics and publishes a weekly report about the number of cases of specific diseases. The World Health Organization (WHO) watches disease patterns worldwide. Some diseases, such as the common cold, are known as endemic diseases. Endemic diseases are continually found in small amounts within the population. A large outbreak of the same disease in an area is an epidemic. If an epidemic is widespread through a large region, such as a country, a continent, or worldwide, it is called a pandemic. 7. Contrast How is a pandemic different from an epidemic? Treating and Fighting Diseases Doctors might prescribe a drug, such as an antibiotic, to help the body fight a disease. A substance that can kill or slow the growth of other microorganisms is an antibiotic (an ti bi AH tihk). Many fungal secretions, such as penicillin, are used as antibiotics. Other antibiotics are manufactured. Over the last 60 years, the widespread use of antibiotics has caused many bacteria to become resistant to particular antibiotics. Resistance develops through natural selection. Some bacteria in a population might have a trait that enables them to survive a particular antibiotic. These surviving bacteria reproduce and pass on this trait. Because bacteria can reproduce quickly, the number of resistant bacteria in a population can increase quickly as well. The figure below shows the rise in the United States of penicillin-resistant gonorrhea (gah nuh REE uh). Picture This 8. Compare Penicillinresistant gonorrhea increased most rapidly between which two years? (Circle your answer.) a and 1982 b and 1989 c and 1990 biologygmh.com Chapter 37 Immune System 437

6 37 Immune System section 2 The Immune System Components of the immune system are nonspecific immunity and specific immunity. What You ll Learn the structure and function of the lymphatic system the difference between passive and active immunity Before You Read Think about the last time you had a cut or scrape. On the lines below, describe how your body responded to the injury. What did the site look like? How did it feel? Read the section to learn how your body fights against infection. Restate the Main Point As you read the section, highlight the main point in each paragraph. Then restate each main point in your own words. 1. Explain how coughing benefits the body. Read to Learn Nonspecific Immunity At birth, the body s immune system has defenses to fight pathogens. These defenses are nonspecific they do not target a specific pathogen. They protect against any pathogen. Nonspecific immunity helps prevent disease. It also helps to slow the progress of a disease while specific immunity begins to develop its defenses. Nonspecific immunity works quickly, but specific immunity is more effective. What barriers protect the body from pathogens? The body s main barrier against infection is the unbroken skin and skin oils. The layers of dead cells covering the skin s living cells help protect against invasion by microorganisms. Many bacteria live on the skin. These bacteria digest skin oils, producing acids that block pathogens. The body also has chemical barriers. Saliva, tears, and nasal secretions contain the enzyme lysozyme. Lysozyme kills bacteria. Mucus, secreted by inner body surfaces, prevents bacteria from sticking to epithelial cells. The beating motion of cilia inside the airway sends bacteria caught in mucus away from the lungs. Extra mucus is secreted after infection, which triggers coughing and sneezing to help move infected mucus out of the body. Stomach acid kills many microorganisms found in food. 438 Chapter 37 Immune System Reading Essentials

7 What if pathogens get past the barriers? When pathogens get through the barriers, the body s nonspecific immunity continues the defense. Cellular Defense If foreign microorganisms enter the body, the cells of the immune system defend the body. One defense is phagocytosis (fa guh si TOH sus) by which white blood cells, especially neutrophils and macrophages, surround and take in foreign microorganisms. The phagocytes then release chemicals that destroy the microorganisms. Blood plasma contains approximately 20 complement proteins. Complement proteins aid phagocytosis by helping phagocytes bind more efficiently to pathogens, activating the phagocytes and enhancing the destruction of the pathogen s membrane. Phagocytes are activated by materials in the bacteria s cell walls. 2. Describe the process of phagocytosis. Interferon When a virus enters the body, interferon helps prevent the virus from spreading. Interferon is a protein secreted by virus-infected cells. Interferon binds to neighboring cells and causes these cells to produce antiviral proteins. Antiviral proteins can prevent virus cells from multiplying. Inflammatory Response When pathogens damage tissue, both the invading pathogen and the cells of the body release chemicals. These chemicals attract phagocytes, increase blood flow to the infected area, and make blood vessels more permeable to allow white blood cells to escape into the infected area. The result is an accumulation of white blood cells to fight the infection. Pain, heat, and redness in the infected area are the result of the inflammatory response. Specific Immunity When pathogens get past the nonspecific defenses, the body has a second line of defense the lymphatic (lim FA tihk) system. The lymphatic system is the body s specific immunity. It attacks the pathogen directly. Specific immunity is more effective but takes more time to develop. What are the functions of the lymphatic system? The lymphatic system filters lymph and blood and destroys foreign microorganisms. Lymph leaks out of capillaries to bathe body cells. After the fluid circulates among the cells, lymphatic vessels collect and return it to the veins near the heart. 3. Identify the system that provides specific immunity. Reading Essentials Chapter 37 Immune System 439

8 4. Explain the role of lymphocytes. What organs are part of the lymphatic system? The figure below shows the organs of the lymphatic system. The organs of the lymphatic system contain lymphatic tissue, lymphocytes, a few other cell types, and connective tissue. Lymphocytes are a type of white blood cell that is produced in red bone marrow. The blood carries them to lymphatic organs. Lymphocytes play a role in specific immunity. The lymph nodes are located in different places along the path of the lymphatic vessels. Lymph nodes filter the lymph and remove foreign materials. The tonsils form a protective ring between the nose and mouth. The spleen stores blood and destroys damaged red blood cells. Lymphatic tissue within the spleen also responds to foreign substances in the blood. The thymus gland, located above the heart, helps to activate a special kind of lymphocyte called a T cell. T cells are produced in the bone marrow, but they mature in the thymus gland. Picture This 5. Label Write these three labels next to the appropriate structures in the diagram. Label: produces T cells Label: activates T cells Label: destroys damaged red blood cells 440 Chapter 37 Immune System Reading Essentials

9 B Cell Response When an antigen, or foreign substance, enters the body, it triggers the production of antibodies. Antibodies are proteins produced by B lymphocytes that specifically react with the antigen. B lymphocytes, or B cells, are antibody factories located in all lymphatic tissues. The figure below shows how B cells are activated to produce antibodies. When a macrophage surrounds, takes in, and digests a pathogen, it displays a piece of the pathogen, called a processed antigen, on its membrane. In lymphatic tissues, the macrophage, with the process antigen on its surface, binds to a type of lymphocyte called a helper T cell. This process activates the helper T cell. The activated helper T cell then activates B cells and another type of T cell to produce antibodies. B cells make many types of antibodies. Antibodies help to kill microorganisms in two ways. Antibodies bind to the microorganisms, making phagocytosis more likely. They can also trigger an inflammatory response. Picture This 6. Determine By what process does the B cell divide? Antigen is engulfed. Antibody-Mediated Response Macrophage Macrophage Activated B cell Activated B cells divide. Processed antigen B cells continue to divide and produce antibodies. Processed antigen Helper T cell C The activated helper T cell presents a processed antigen to B cells. The B cell divides by mitosis. D Some activated B cells remain as memory B cells. The daughter B cells continue to divide and produce antibodies. Some of these daughter B cells remain as memory cells in case the body encounters this same pathogen again. A B A macrophage engulfs an antigen. It places a portion of the antigen outside the cell, held in place by a receptor. The macrophage presents the antigen to the helper T cell by binding to a receptor on the helper T cell. This binding helps the helper T cell divide. D Antigen is engulfed. The activated cytotoxic T cell binds to and kills antigen presenting (infected) cells. Cytotoxic T-Cell Response Macrophage Macrophage Cytotoxic T cell Processed antigen Antigen on infected cell Processed antigen C Infected cell lyses. Helper T cell The activated helper T cell presents a processed antigen to the cytotoxic T cell, activating it to divide and secrete cytokines. Activated cytotoxic T cells divide. Some cytotoxic T-cells release cytokines. Reading Essentials Chapter 37 Immune System 441

10 Take Notes Make a two-tab Foldable, as shown below. As you read, take notes and organize what you learn about active and passive immunity. Active Immunity Passive Immunity 7. Draw Conclusions Many AIDS patients die of diseases unrelated to HIV. Why do you think this happens? T Cell Response Once activated, helper T cells can activate lymphocytes called cytotoxic T cells. Activated cytotoxic T cells destroy pathogens and release chemicals called cytokines. Cytokines stimulate cells of the immune system to divide and attract immune cells to the infected area. Passive and Active Immunity When a virus enters the body, nonspecific and specific immunity respond and defeat the pathogen. This is the body s first, or primary, response. A result of this response is the production of memory B and T cells. Memory cells are longliving cells that are exposed to the antigen during the primary immune response. If the body is later exposed to the same pathogen, memory cells respond rapidly to protect the body. How is passive immunity produced? Passive immunity provides temporary protection against an infection. Antibodies made by other people or animals can be transferred, or injected, into the body. For example, a mother s antibodies transfer to her child through the placenta and breast milk. Antibodies from an immune person or animal can be injected into another person s body. How does active immunity develop? Active immunity occurs when exposure to disease antigens causes memory cells to be produced. Active immunity can result from having an infectious disease or from immunization. Immunization, or vaccination, is intentional exposure to an antigen so that a primary response and immune memory will develop. Immunizations contain killed or weakened pathogens that can stimulate an immune response and memory cells without causing the disease. Immune System Failure Some diseases reduce the immune system s effectiveness. One such disease, acquired immunodeficiency syndrome (AIDS), results from infection by human immunodeficiency virus (HIV). HIV infects helper T cells, turning them into HIV factories. The new viruses then infect other helper T cells. Over time, loss of helper T cells reduces the body s ability to fight off diseases. Patients might exhibit few symptoms for as many as ten years but can still spread the infection through sexual intercourse or blood. 442 Chapter 37 Immune System biologygmh.com

11 37 Immune System section 3 Noninfectious Disorders Before You Read Do you or a friend have an allergy? On the lines below, describe the symptoms. Read the section to learn the causes of common noninfectious disorders such as allergies. There are five categories of noninfectious diseases. What You ll Learn the role of allergens in allergies the difference between allergies and anaphylactic shock Read to Learn Genetic Disorders Not all disorders are caused by pathogens. Some result from defective genes or chromosomes. Other disorders have both a genetic and an environmental cause. One example is coronary artery disease (CAD). Inherited genes increase the risk of developing CAD. Environmental factors, such as diet, contribute to the development of the disease. Degenerative Diseases Degenerative diseases (dih JEH nuh ruh tihv dih ZEEZS) result from part of the body deteriorating. Degenerative arthritis and arteriosclerosis (ar tir ee oh skluh ROH sus) are two examples. Degenerative arthritis is common. Most people have it by age 70. Inherited genes can make some individuals more likely to develop degenerative diseases. Metabolic Diseases Metabolic disease results from an error in a biochemical pathway, such as an inability to regulate body processes. One example is Type I diabetes. The pancreas does not make the proper amount of insulin. The result is too much glucose in the blood, which damages many organs. Metabolic diseases can have genetic and environmental components. Make Flash Cards Make a flash card for each category of disorder as you read about it. On the back of the flash card, list the characteristics of diseases in that category. Use the flash cards to review what you have learned. 1. Describe the body process that does not function properly in Type I diabetes. Reading Essentials Chapter 37 Immune System 443

12 Cancer Cancer is abnormal cell growth. Normally, the body can control cell division. If this control is lost, abnormal cell growth results, which can lead to tumors. The abnormal cells can interfere with normal body functions and travel throughout the body. Cancer tumors can develop in any tissue or organ. Cancer in blood cells is called leukemia. Both genes and the environment contribute to cancer. 2. Identify Where can cancer tumors develop? 3. Compare How does anaphylactic shock differ from more common allergic reactions? Inflammatory Diseases Inflammatory diseases, such as allergies, result when the body produces an inflammatory response to a common substance. When the body responds to an infectious disease, the inflammatory response helps fight the disease. In inflammatory disease, the inflammatory response does not help the body. What can cause allergies? An allergy is an abnormal response to antigens in the environment. These antigens, called allergens, include plant pollens, dust, dust mites, and some foods. Symptoms may include itchy eyes, stuffy nose, sneezing, and sometimes a skin rash. The symptoms result from the chemical histamine that is released by certain white blood cells. Anaphylactic (an uh fuh LAK tik) shock is a severe allergic reaction, resulting in a massive release of histamine. The smooth muscles in the bronchioles contract, restricting air flow into and out of the lungs. Severe reactions can result from bee stings, penicillin, peanuts, or latex, which is a substance used to make balloons and surgical gloves. Anaphylactic shock can be life threatening. Allergies and anaphylactic reactions are genetic. How does the body respond in autoimmunity? The immune system normally learns to tolerate self and will not attack self-proteins. However, some people develop autoimmunity (aw toh ih MYOON ih tee) and form antibodies to their own proteins, which injure their cells. In rheumatoid (roo MAH toyd) arthritis, antibodies attack the joints. In rheumatic fever, antibodies attack the valves of the heart causing the valves not to close properly. In lupus (LEW pus), antibodies attack cell nuclei, resulting in damage to many organs. 444 Chapter 37 Immune System biologygmh.com