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Ch 43 The Immune System (Adv Bio bk)

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II. Defenses Against Infection A. Nonspecific Defenses 1. First Line of Defense a. skin

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b. openings of body are protected by 1) saliva, mucus, and tears contain lysozyme which breaks down bacterial cell walls 2) mucus in nose and throat trap pathogens cilia push away from the lungs 3) stomach secretions destroy many pathogens that are swallowed

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2. Second Line of Defense a. Inflammatory Response 1) pathogens stimulate mast cells to release chemicals called histamines a) histamines increase the flow of blood and fluids to the affected area

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2) Fluid leaking from expanded blood vessels causes the area to swell

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3) White blood cells (Leukocytes) move from blood vessels into infected tissues

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4) Phagocytes (ie macrophages) engulf and destroy bacteria

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5) All this activity can increase local temperature

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b. Interferons 1) proteins that inhibit synthesis/production of viral proteins 2) allow time for specific immune defenses to respond and fight the infection

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c. Fever 1) immune system releases chemicals that increase body temperature 2) increased body temperature slows or stops growth of some pathogens 3) increased body temperature speeds up several parts of the immune response

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B. Specific Defenses of the Immune System 1. specific defenses a. distinguish self and others 1) immune system recognizes chemical markers that act like secret passwords 2) others lack the correct chemical markers b. inactivates or kills any foreign substance that enters the body c. responds to a particular pathogen

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2. Antigens a. any foreign substance (protein or polysaccharide) that can stimulate an immune response b. usually located on the outer surfaces of bacteria, viruses, or parasites

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3. Antibodies a. proteins that tag antigens for destruction by immune cells b. circulate in blood or lymph may be attached to immune cells or free-floating in plasma c. body can make up to 10 billion different antibodies 1) amino acid sequences differ from cell to cell d. the shape of each type of antibody allows it to bind to one specific antigen

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4. Lymphocytes (a type of WBC) B Cells T Cells

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4. Lymphocytes (a type of WBC) a. B Lymphocytes B Cells (B = bone marrow) 1) produced in and mature in red bone marrow 2) embedded antibodies are Y shaped a) the shape of the binding sites enable an antibody to recognize a specific antigen with a complementary shape 3) discover antigens in body fluids

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b. T Lymphocytes T cells (T = thymus) 1) produced in bone marrow, but mature in thymus 2) must be presented with an antigen by infected body cells or immune cells that have encountered antigens

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c. B Cells and T Cells 1) capable of recognizing only one specific antigen specific receptor 2) travel to lymph nodes and spleen where they encounter antigens 3) one B or T cells bears 100,000 antigen receptors they are all the same

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C. The Immune System in Action 1. Humoral Immunity 2. Cell-Mediated Immunity

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C. The Immune System in Action 1. Humoral Immunity a. involves the activation and clonal selection of B cells resulting in production of secreted antibodies or immunoglobulines that circulate in blood or lymph b. antigens on the surface of pathogens bond to antibodies on B cells c. then, T cells stimulate the B cell to grow and divide rapidly

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d. This produces two types of B cells Plasma cells Memory cells

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d. This produces two types of B cells 1) plasma cells a) produce and release antibodies that are carried through the bloodstream b) recognize and bind to free-floating antigens or to antigens on the surface of pathogens c) this signals other types of cells and proteins to attack and destroy the invaders d) they die after infection is gone

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2) Memory B Cells a) stay alive after an infection is gone b) they react quickly if the same pathogen enters the body again c) rapidly produce plasma cells d) second response is faster than the first

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2. Cell-Mediated Immunity a. involves the activation and clonal selection of cytotoxic T cells which directly destroy certain target cells b. defends the body against some viruses, fungi, and single-celled pathogens c. when a cell is infected by a pathogen or when a macrophage consumes a pathogen, the cell destroys a portion of the antigen on the outer surface of its membrane d. this signals helper T cells to divide

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e. Helper T cells activate B cells, cytotoxic T cells and produce memory T cells 1) cytotoxic T cells a) hunt down infected body cells and kill them b) puncture cell membranes and initiate apoptosis (programmed cell death)

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2) Memory T cells a) help the immune system respond quickly the second time 3) Suppressor T cells a) inhibit the immune system once an infection is under control b) help prevent autoimmune diseases

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III. Fighting Infectious Diseases A. Active Immunity 1. natural exposure to antigen (fighting an infection) or deliberate exposure to an antigen (through a vaccine) 2. when the immune system is exposed to antigens a. memory B cells are produced b. memory T cells are produced 3. this quickens and strengthens the bodys responses to repeated infections

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B. Passive Immunity 1. externally produced antibodies are introduced into a persons blood 2. lasts only a short time because the immune system eventually destroys the foreign antibodies

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Hi

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