1. Ch. 21 Infectious Diseases
Section 2- Defense Against Disease

2. Section 2- Defense Against Disease
Section 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.

3. Section 2- Defense Against Disease
Physical and Chemical Defenses If pathogens are everywhere, why aren’t you sick all the time? Your body’s first line of defense against infectious disease includes both physical and chemical defenses that prevent pathogens from entering your body. Review Figure 3 on pg. 553

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Physical & Chemical Defenders Your body is a castle- the skin, a physical defense, is wall surrounding the castle. The wall prevents invaders from getting into the castle. Chemical defenses are the Knights who fight invaders who manage to penetrate the castle walls.

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Physical and Chemical Defenses Skin: -a physical and chemical barrier against pathogens. The surface cells are hard and have no gaps between them. -sweat acts as a chemical barrier because it contains acids that kill many bacteria. -microorganisms usually cannot get through your skin unless you have a cut, scrape, burn or other injury.

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Physical and Chemical Defenses Membranes: -the protective linings along all the tubes and cavities that lead outside the body, such as your mouth, eyes, and nose. -Mucous membranes secrete a liquid called mucus. The mucus traps many pathogens and washes them away. -Mucus also contains chemicals that attack pathogens.

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Physical and Chemical Defenses Cilia: -Some of your body’s mucous membranes are lined with tiny hair-like structures called cilia. -Cilia and mucus work together to trap and remove pathogens, as example, when you inhale dust and pathogens get trapped in the mucus of your airway. The cilia moves the mucus toward your mouth & nose. (cough or sneeze)

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Physical and Chemical Defenses Saliva & Tears: -traps pathogens and washes them away. -contains chemicals that attack pathogens Digestive System: -Chemicals in your digestive system, including acids in your stomach, kill many pathogens. The normal process of your digestive system not only moves food through your body, but also moves pathogens out.

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Inflammation: -the second line of defense -your body’s general response to all kinds of injury, from cuts and scrapes to internal damage. -fights infection and promotes the healing process.

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Inflammation: Phagocytes: Greek-phago = “to eat” cyte = cell - a type of white blood cell that engulfs and destroys pathogens. -within seconds after your body is injured, the damaged cells release chemicals that cause blood vessels in the injured area to enlarge. -the infected area becomes red, swollen, and sore

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Inflammation: Healing: -the fluids, phagocytes, and dead cells that accumulate at the injury site often result in the formation of a thick, white liquid called pus.

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The Immune System: -fights disease by producing a separate set of weapons for each kind of pathogen it encounters. Consider the meaning of the word- Immunity What might happen if the immune system was not able to function properly in a person’s body?

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The Immune Response: -to fight disease, your immune system must build up its arsenal of weapons against invading pathogens. This process takes time, during which the pathogen multiples in your body and causes disease. Lymphocytes: -white blood cells that carry out the functions of the immune system

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The Immune Response: What happens 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- your body’s ability to destroy pathogens that it has previously encountered before the pathogens are able to cause disease.

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The Immune Response: - There are two types of lymphocytes- T lymphocytes / T cells B lymphocytes / B cells

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The Immune Response:
T Cells:
-perform several functions:
Killer T cells: destroy any body cells 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.

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The Immune Response: B cells: -produce antibodies Antibodies- proteins that attach to the surface of pathogens or to the toxins produced by pathogens.

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The Immune Response: The Lymphatic System: -much of your immune system is contained in your lymphatic system -The Lymphatic system is a network of vessels that collects fluid from your tissues and returns it to the bloodstream.

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Passive and Active Immunity: -both types are important in protecting your body against infections. Passive Immunity: -immunity acquired by receiving antibodies from a source other than one’s own immune system. -Example- babies receive this from their mother’s breast milk -Example- rabies antibodies

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Active Immunity: -results from either having a disease or receiving a vaccine Immunization: an injection that causes the body to become immune to an infectious disease. Vaccine: the substance that is injected. -contains small amounts of dead or modified pathogens or their toxins

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