1. Section 21.2 Defenses Against Disease Slide 1 of 28 For each of your responses, explain how your behavior could affect your chances of getting or spreading an infectious disease. Quick Quiz Complete each of these statements with always, sometimes, or never. I ____ wash my hands before meals. When preparing fruits and vegetables, I ____ wash them thoroughly. I am ____ careful to use only my own eating utensils, drinking cups, towels and grooming items. I ____ cover my mouth when I cough or sneeze. If I spend time in wooded areas, I ____ wear insect repellent.

2. Section 21.2 Defenses Against Disease Slide 2 of 28 Your body’s first line of defense against infectious disease includes both physical and chemical defenses that prevent pathogens from entering your body. Physical and Chemical Defenses

3. Section 21.2 Defenses Against Disease Slide 3 of 28 Your skin serves as both a physical and a chemical barrier against pathogens. Skin Sweat acts as a chemical barrier. Old skin cells are shed constantly, and the pathogens on these cells are shed, too.

4. Section 21.2 Defenses Against Disease Slide 4 of 28 The openings into your body, such as your mouth, eyes, and nose, are covered by protective linings called mucous membranes (MYOO kus). Mucous Membranes Mucus traps many pathogens and washes them away. Mucus contains chemicals and specialized cells that attack pathogens.

5. Section 21.2 Defenses Against Disease Slide 5 of 28 Some of your body’s mucous membranes are lined with tiny hairlike structures called cilia (SIL ee uh). Cilia Together, cilia and mucus help trap and remove pathogens.

6. Section 21.2 Defenses Against Disease Slide 6 of 28 Your saliva and tears can trap pathogens and wash them away. Saliva and Tears Saliva and tears also contain chemicals that attack pathogens.

7. Section 21.2 Defenses Against Disease Slide 7 of 28 Chemicals in your digestive system kill many pathogens. Digestive System The normal motions of the digestive system move pathogens out. Bacteria that normally live in your digestive system produce substances that can harm or kill invading bacteria.

8. Section 21.2 Defenses Against Disease Slide 8 of 28 1)Saliva and tears Saliva and tears can wash away some pathogens. 2)Mucous membranes Mucus traps some pathogens, preventing them from entering your body. 3)Cilia Cilia help move mucus and pathogens out of your body when you cough or sneeze. Your Body’s Physical and Chemical Defenses 4)Skin Your skin is an effective barrier against many pathogens. 5)Stomach acid When you swallow certain pathogens with food, water, or mucus, acids in your stomach can kill those pathogens.

9. Section 21.2 Defenses Against Disease Slide 9 of 28 Inflammation (in fluh MAY shun) is your body’s general response to all kinds of injury, from cuts and scrapes to internal damage. Inflammation Inflammation fights infection and promotes the healing process.

10. Section 21.2 Defenses Against Disease Slide 10 of 28 Within seconds after your body is injured, the damaged cells release chemicals that cause blood vessels in the injured area to enlarge. Phagocytes Blood, other fluids, and white blood cells called phagocytes (FAG uh syts) leak out of the enlarged vessels. Phagocytes engulf and destroy pathogens.

11. Section 21.2 Defenses Against Disease Slide 11 of 28 This micrograph shows a phagocyte (blue) attacking bacteria (pink). Phagocytes kill pathogens by engulfing and then digesting them. Phagocytes

12. Section 21.2 Defenses Against Disease Slide 12 of 28 Phagocytes also give off substances that cause healing to begin. Healing The inflammation process heals the damage, and the inflammation subsides.

13. Section 21.2 Defenses Against Disease Slide 13 of 28 The immune system (ih MYOON) fights disease by producing a separate set of weapons for each kind of pathogen it encounters. The Immune System

14. Section 21.2 Defenses Against Disease Slide 14 of 28 When a pathogen enters your body for the first time, it often causes disease. The Immune Response If a pathogen that has previously attacked your body enters your body again your immune system will quickly recognize the pathogen and launch an immediate attack. Immunity (ih MYOON ih tee) is your body’s ability to destroy pathogens that it has previously encountered before the pathogens are able to cause disease. White blood cells called lymphocytes (LIM fuh syts) carry out most of the immune system’s functions.

15. Section 21.2 Defenses Against Disease Slide 15 of 28 T cells perform several functions. T Cells Helper T cells produce chemicals that stimulate other T cells and B cells to fight off infection. Suppressor T cells produce chemicals that “turn off” other immune system cells when an infection has been brought under control. Killer T cells destroy any body cell that has been infected by a pathogen.

16. Section 21.2 Defenses Against Disease Slide 16 of 28 The B lymphocytes, or B cells, produce antibodies. B Cells This binding action keeps the pathogen or toxin from harming the body. The memory capacity of B cells explains why you develop immunity to some diseases you’ve already had. Antibodies (AN tih bahd eez) are proteins that attach to the surface of pathogens or to the toxins produced by pathogens.

17. Section 21.2 Defenses Against Disease Slide 17 of 28 The Immune Response

18. Section 21.2 Defenses Against Disease Slide 18 of 28 The lymphatic system (lim FAT ik) is a network of vessels that collects fluid from your tissues and returns it to the bloodstream. The Lymphatic System The lymphatic vessels have hundreds of small stations, called lymph nodes. The fluid flowing through the lymphatic system is called lymph (limf).

19. Section 21.2 Defenses Against Disease Slide 19 of 28 Lymph nodes Lymph vessel Your lymphatic system is a complex network of vessels and nodes. The Lymphatic System

20. Section 21.2 Defenses Against Disease Slide 20 of 28 Immunity acquired by receiving antibodies from a source other than one’s own immune system is called passive immunity. Passive and Active Immunity This type of immunity is temporary, not lifelong. Passive Immunity It occurs naturally in babies, who receive antibodies from their mothers before birth. Passive immunity can be artificially acquired.

21. Section 21.2 Defenses Against Disease Slide 21 of 28 Active immunity results from either having a disease or from receiving a vaccine. Passive and Active Immunity Injections, which cause you to become immune to a disease, are called immunizations (im yuh nih ZAY shunz), or vaccinations. Active Immunity The substance that is injected is called a vaccine (vak SEEN). Vaccines contain small amounts of dead or modified pathogens or their toxins.