Section 21.2 Defenses Against Disease Objectives Identify the body’s physical and chemical defenses against infectious disease. Describe the inflammatory response. Summarize how the immune system works. Compare passive and active immunity.

I ____ wash my hands before meals. 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. For each of your responses, explain how your behavior could affect your chances of getting or spreading an infectious disease. Switch to QuickTake version of the quiz.

Physical and Chemical Defenses Your body’s first line of defense against infectious disease includes both physical and chemical defenses that prevent pathogens from entering your body.

Skin Your skin serves as both a physical and a chemical barrier against pathogens. Sweat acts as a chemical barrier. Old skin cells are shed constantly, and the pathogens on these cells are shed, too.

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

Cilia Some of your body’s mucous membranes are lined with tiny hairlike structures called cilia (SIL ee uh). Together, cilia and mucus help trap and remove pathogens.

Saliva and Tears Your saliva and tears can trap pathogens and wash them away. Saliva and tears also contain chemicals that attack pathogens.

Digestive System Chemicals in your digestive system kill many pathogens. 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.

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

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

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

Phagocytes This micrograph shows a phagocyte (blue) attacking bacteria (pink). Phagocytes kill pathogens by engulfing and then digesting them.

Healing Phagocytes also give off substances that cause healing to begin. The inflammation process heals the damage, and the inflammation subsides.

The Immune System The immune system (ih MYOON) fights disease by producing a separate set of weapons for each kind of pathogen it encounters.

The Immune Response When a pathogen enters your body for the first time, it often causes disease. White blood cells called lymphocytes (LIM fuh syts) carry out most of the immune system’s functions. 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.

For: More on the immune response Click above to go online.

T Cells T cells perform several functions. Killer T cells destroy any body cell that has been infected by a pathogen. 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.

B Cells The B lymphocytes, or B cells, produce antibodies. Antibodies (AN tih bahd eez) are proteins that attach to the surface of pathogens or to the toxins produced by pathogens. 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.

The Immune Response

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

Lymph nodes Lymph vessel The Lymphatic System Your lymphatic system is a complex network of vessels and nodes.

Active Art: Immune response Click on the screen above to launch the Active Art.

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

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

Vocabulary mucous membrane The protective lining that covers any opening into the body. inflammation The body’s general response to all kinds of injury. phagocyte A type of white blood cell that engulfs and destroys pathogens. immune system The body’s most sophisticated defense against pathogens. lymphocyte A type of white blood cell that carries out functions of the immune system.

Vocabulary immunity The body’s ability to destroy a pathogen that it has previously encountered before the pathogen is able to cause disease. T cell A type of lymphocyte that helps the immune system destroy pathogens. B cell A lymphocyte that produces antibodies. antibody A protein that attaches to the surface of pathogens or to the toxins produced by pathogens, keeping the pathogen or toxin from harming the body.

Vocabulary lymphatic system A network of vessels that collects fluid from body tissues and returns it to the bloodstream; contains much of the immune system. immunization An injection that causes the body to become immune to an infectious disease; also called a vaccination. vaccine A substance containing small amounts of dead or modified pathogens or their toxins that is injected during an immunization.

QuickTake Quiz Click to start quiz.

End of Section 21.2 Click on this slide to end this presentation.