The Immune System

1. The Immune System In this lesson, you will Learn About… • The function of the immune system. • How antibodies protect the body from pathogens. • How you can develop immunity to a disease.

2. The Immune System The Vocabularyterms in this lesson are: • Immune system. • Inflammation. • Lymphatic system. • Lymphocytes. • Antigens. • Antibodies. • Immunity. • Vaccine.

3. Keeping Pathogens Out Each day you are exposed to countless pathogens. Your body can repel, trap, or destroy most of these pathogens before they can do any damage. The five major barriers against such invaders help keep pathogens out.

4. Tears Tears wash away pathogens. They also contain chemicals that kill some harmful organisms. Mucous Membranes These tissues line your mouth, nose, throat, eyes, and other body openings. They trap pathogens. When you cough or sneeze, you expel the pathogens trapped by the mucous membranes in your nose and throat. Saliva Saliva in your mouth destroys many harmful organisms. Stomach Acid The acid in your stomach destroys many pathogens. Skin Your skin acts as a protective barrier. Pathogens may get through this barrier when you have a cut, burn, or scrape. The Five Major Barriers

5. The Immune System’s Nonspecific Response If pathogens enter the body, the immune system launches an attack. The immune system’s nonspecific response is always the same, regardless of the type of foreign substance that invades the body. The inflammatory response is a nonspecific response that occurs if a foreign invader gets past the five major barriers.

6. The Immune System’s Nonspecific Response (cont’d.) The steps of the inflammatory response: • The blood supply to the affected area increases, and circulation in that area slows down. • This raises the blood pressure in the area, causing fluid to leak from the blood vessels. • As a result, surrounding tissues swell. • Special white blood cells called phagocytes attack the invading pathogens. • The phagocytes surround the invaders, take them apart, and “eat” them.

7. The Immune System’s Nonspecific Response (cont’d.) Other components of the inflammatory response: • The phagocytes release special proteins to help defend the body. One of these proteins, interferon, stops viruses from reproducing and helps the cells that fight infection. • If the infection has spread throughout the body, a fever becomes part of the inflammatory response.

8. Inflammation During the inflammatory response, more blood flows to the infected area, and phagocytes rush in to destroy the invading pathogens. Phagocyte Pathogen Splinter Pathogen Phagocyte Blood vessel

9. The Immune System’s Specific Responses When pathogens survive the inflammatory response, the body counters with a specific response. This response: • Is tailored to a particular pathogen and the poisons that it produces. • Not only defends the body against an invading pathogen, but also allows the immune system to “remember” that particular type of pathogen.

10. The Lymphatic System The lymphatic system is a secondary circulatory system that helps your body fight pathogens and maintain its fluid balance. Your body calls upon the lymphatic system to fight against specific pathogens.

11. The Lymphatic System (cont’d.) The lymphatic system circulates a watery fluid known as lymph. Special white blood cells in the lymph are called lymphocytes. There are three types: • B cells • T cells • NK cells

12. The Lymphatic System (cont’d.) The lymph also contains phagocytes called macrophages that digest and process the invading pathogens and then help the lymphocytes identify them. The three types of lymphocytes are activated when the body recognizes a part of a pathogen known as an antigen.

13. Antibodies Your body reacts to antigens by producing antibodies. Antibodies are proteins that attach to antigens, keeping them from harming the body. B cells produce specific antibodies to fight a particular type of antigen.

14. The Immune System’s Response to Infection • A macrophage engulfs one of the pathogens and presents its antigens to the T cells, which identify the pathogen as an invader. • T cells multiply at the site of the infection. The T cells activate the B cells. • A pathogen invades the body. The antigens in the pathogen activate the immune system’s response.

15. The Immune System’s Response to Infection (cont’d.) • Memory T cells and B cells remain in the system. The next time this type of pathogen enters the system, these memory cells attack it swiftly. • B cells multiply. • The B cells release antibodies, which attach themselves to the antigens. Special T • cells attack and destroy the invaders. • Some B cells and T cells become memory cells.

16. Immunity Your body’s ability to resist the pathogens that cause a particular disease is called immunity. You were born with some immunities that were passed on to you from your mother. These immunities lasted for a few months, after which you began to produce antibodies on your own.

17. Immunity (cont’d.) Another way your body builds immunity is by being exposed to pathogens and by having certain diseases. When your body encounters an antigen, it produces memory B cells and T cells. Often these memory cells stay in the blood. If the same type of pathogen returns, the immune system fights it so that you do not become ill a second time.

18. Immunity (cont’d.) You don’t have to get a disease to acquire immunity to it. You can receive an immunization, or vaccine. This process is called immunization because the antibodies your body produces in response to the vaccine will build immunity.

19. Reviewing Terms and Facts • Define the term immune system. The immune system is a combination of body defenses made up of cells, tissues, and organs that fight off pathogens.

20. Reviewing Terms and Facts • What are the body’s five major barriers against pathogens? • Tears • Saliva • Skin • Mucous membranes • Stomach acid

21. Thinking Critically • Why do you think diseases that damage the immune system are so dangerous to the body?

22. Vocabulary Review The immune system is a combination of body defenses made up of cells, tissues, and organs that fight off pathogens.

23. Vocabulary Review Inflammation is the body’s response to injury or disease, resulting in a condition of swelling, pain, heat, and redness.

24. Vocabulary Review The lymphatic system is a secondary circulatory system that helps the body fight pathogens and maintain its fluid balance.

25. Vocabulary Review Lymphocytes are special white blood cells in the lymph.

26. Vocabulary Review Antigens are substances that send the immune system into action.

27. Vocabulary Review Antibodies are proteins that attach to antigens, keeping them from harming the body.

28. Vocabulary Review Immunity is the body’s ability to resist the pathogens that cause a particular disease.

29. Vocabulary Review A vaccine is a preparation of dead or weakened pathogens that is injected into the body to cause the immune system to produce antibodies.