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Transcript
1. 40–2 The Immune System The function of the immune system is to fight infection through the production of cells that are able to identify and destroy foreign cells and materials that do not belong in the body. This system relies on a series of different cells that can recognize, attack, destroy, and “remember” each type of pathogen, something that can make you sick, that enters the body. This process is called immunity. The immune system has nonspecific defenses to stop pathogens from entering the body or attacks all pathogens the same way. These defenses include physical and chemical barriers. • First line of defense. The function of the first line of defense is to keep pathogens out of the body. This role is carried out by skin, mucus, sweat, and tears. Your body’s most important nonspecific defense is the skin. It forms a barrier that few pathogens can get through. Mucus, saliva, and tears trap pathogens and contain an enzyme that kills bacteria. • Second line of defense. When pathogens do enter the body, other nonspecific defenses go to work. The inflammatory response is a nonspecific defense reaction to tissue damage caused by injury or infection. Blood vessels near the wound expand. Specialized white blood cells called macrophages, enter the tissues to fight infection. Macrophages look for and identify foreign materials based on unique proteins and carbohydrates these materials carry. The unique proteins and carbohydrates a cell or virus has is called antigens when the immune system starts to attack them. After the macrophage attacks and destroys the foreign cell,the macrophage takes the antigen to the B cells and T cells to begin the specific part of the immune response. A fever, or higher than normal body temperature, can slow pathogen growth. A fever serves to slow the reproduction of the pathogen (usually a virus or bacteria) so the immune system has a better chance of removing them. If a pathogen gets past the nonspecific defenses or continues to grow in number, specific immune defenses go to work. This is called the immune response. There are two types of immune response. • In humoral immunity, white blood cells, called B cells, make unique proteins called antibodies that attack the pathogen in the blood. Antibodies are proteins that recognize and bind to the antigens found on the surface of the pathogens. Each B Cell is only able to produce one type of antibody. Different antibodies must be made for each different pathogen that enters the body • In cell-mediated immunity, white blood cells, called helper T cells, find and destroy abnormal or infected cells. Helper T cells are specific to the pathogen they can recognize. Each helper T cell can only recognize one antigen or pathogen. When the correct helper T cell is found, the helper T cells activates cytotoxic (killer) T Cells. Cytotoxic T Cells multiply and travel in the blood stream looking for any cells with the antigen. When the antigen is found, the cell is destroyed. After a pathogen is destroyed, memory cells are formed. These cells respond if the same pathogen enters the body again. Both B cells and T cell form memory cells so that the body can fight off the pathogen more quickly in the future. Having memory cells give an individual immunity to the disease. You can acquire immunity without having a disease. Vaccination is the injection of a weakened or mild form of a pathogen to cause immunity. Immunity that results from vaccines is called active immunity. Active immunity appears after exposure to an antigen. Passive immunity forms when antibodies are introduced into the body. Passive immunity lasts only as long as the antibodies stay in the body. Besides vaccinations, bacterial infections can be treated with antibiotics, medications that only harm bacterial cells by destroying their cell walls. Unfortunately, antibiotics have been misused and many types of bacteria have evolved immunity to these antibiotics. Immunodeficiency diseases occur when the immune response breaks down. AIDS is one example of an immunodeficiency disease. AIDS is caused by HIV (human immunodeficiency virus). HIV attaches to receptors on helper T cells. Once inside the cells, HIV copies itself and kills the infected helper T cells. HIV gradually kills off all the helper T cells. As a result, the immune system can no longer fight infections. AIDS can be transmitted from mother to child during pregnancy, childbirth, and breast-feeding. It can also be transmitted from one person to another through shared needles, contact with infected blood, and sexual intercourse. The only no-risk behavior with respect to HIV and AIDS is abstinence. Questions: 1. What is the purpose of the immune system? 2. What can pathogens do to the body? 3. What is the first line of defense for the immune system? 4. When does the second line of defense start? 5. What is the inflammatory response? 6. What is a macrophage? 7. What is an antigen? 8. What does the macrophage do with the antigen? 9. What is the purpose of a fever? 10. Describe humoral immunity? 11. What is an antibody? 12. Describe cell mediated immunity? 13. What is the difference between a helper T cell and a cytotoxic T cell? 14. What are memory cells? 15. How do memory cells give an individual immunity? 16. How does a vaccination help a person? 17. What do antibiotics do? 18. What virus causes AIDS? 19. What does HIV do to the body? 20. How doe HIV spread? For the following statements, match the correct term. Terms may be used more than once, some answers may have more than one answer. Helper T-Cell B-cell Macrophage Skin 21. 22. 23. 24. 25. 26. 27. Divides and activate the cytotoxic Cells Produces antibodies Prevents pathogens from entering the body Activates with specific antigens Tries to stop all pathogens equally Can become a memory cell Produces proteins that attach to antigens Use the graph to answer the following two questions. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. Determine if the following statements are true or false. If false, rewrite the statement to make it correct. An antibody is a protein or carbohydrate an immune cell cannot recognize. Helper T Cells help to activate both B cells and cytotoxic T cells. The skin and B cells are a part of the nonspecific defense. A vaccination can help to produce memory cells. The HIV virus attacks the macrophages of the immune system. An antibody is able to attach to many different antigens. A person can only get immunity to a pathogen by getting sick. Cytotoxic T cells make antibodies. Inflammation causes more macrophages to arrive at a possible infection.