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Chapter 43 Notes The Body’s Defenses
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Nonspecific Defenses Against Infection The skin and mucous membranes provide first-line barriers to infection -skin prevents the entry of pathogens - mucous membranes line digestive and respiratory tracts - the skin also secretes acids and chemicals - lysozyme: digests the cell wall
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Nonspecific Defenses Against Infection Phagocytic cells, inflammation, and antimicrobial proteins function early in infection Mechanisms depend mainly on phagocytosis: the ingestion of invading organisms by certain types of white cells
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Nonspecific Defenses Against Infection - neutrophils: make up 60-70% of WBC; engulf and destroy invaders - monocytes: more effective; develop into macrophages (“big eaters”); will fuse with a lysosome that will release hydrolytic enzymes - natural killer (NK) cells: destroy virus-infected body cells
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Nonspecific Defenses Against Infection
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Damage to tissue triggers a localized inflammatory response - cells release histamine causing dilation of vessels - increased blood supply, due to dilation, causes redness and warmth - blood flow also brings large numbers of phagocytes to the infected area
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Nonspecific Defenses Against Infection
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How Specific Immunity Arises Lymphocytes provide the specificity and diversity of the immune system Two main types: B lymphocytes (B cells) and T lymphocytes (T cells) - recognize and respond to particular microbes and foreign molecules (antigen)
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How Specific Immunity Arises - B cells secrete proteins (antibodies) to fight antigens - T and B cells can distinguish among antigens - each antigen has a particular molecular shape and stimulates certain B cells to secrete antibodies that interact with it
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How Specific Immunity Arises - T and B cells recognize specific antigens by plasma membrane-bound antigen receptors
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How Specific Immunity Arises Antigens interact with specific lymphocytes, inducing immune responses and immunological memory - clonal selection: the cloning of lymphocytes into plasma cells (short- lived) and memory cells (long-lived)
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How Specific Immunity Arises
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Primary immune response: the first time the body is exposed to an antigen - takes 10 to 17 days for effective response to an antigen Secondary immune response: when the individual is exposed to the same antigen at a later date - takes 2 to 7 days
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How Specific Immunity Arises
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Lymphocytes originate from stem cells of the bone marrow - develop into T cells if the continue their development in the Thymus - develop into B cells if they finish development in the bone marrow
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How Specific Immunity Arises
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The immune system exhibits the feature of self-tolerance - major histocompatibility complex (MHC) are a series of glycoproteins that mark the body as “self” - MHC provides a biological fingerprint; found in studying skin graft rejection and acceptance
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How Specific Immunity Arises There are two main types of T cells: cytoxic T cells (T C ) and helper T cells (T H ) Cytoxic T cells have antigen receptors that bind to protein fragments displayed by class I MHC molecules Helper T cells have receptors that bind to peptides displayed by class II MHC
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How Specific Immunity Arises
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Immune Responses In response to antigens, the immune system can mount a humoral response or a cell-mediated response Humoral immunity: involves B cell activation and results from the production of antibodies that circulate in the blood plasma and lymph to attack free antigens
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Immune Responses - B cells form Plasma cells - plasma cells secrete antibodies for an antigen - B cells also give rise to B memory cells - become activated during the second infection
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Immune Responses Cell-mediated immunity: T cells are active against viruses and bacteria that have infected cells; also is crucial in the body’s response against transplanted tissues and cancerous cells - activated T cells become T H or T C ; T H activate B cells that produce antibodies, T C destroy infected body cells
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Immune Responses
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