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Simon Fraser University
Health Sciences
HSCI 100
Nienke Van Houten

Ch 13 – body defense mechanisms FIRST LINE OF DEFENSE – NONSPECIFIC PHYSICAL & CHEMICAL SURFACE BARRIERS - Keep foreign organisms/molecules out of body in first place - Non specific Chemical/physical surface barriers o Tears: wash away irritation, lysozymes kills bacteria o Skin: physical barrier, acidic pH discourages growth of organisms, sweat + oil secretion kill bacteria o Large intestine: normal bacteria keep invaders in check o Saliva: washes microbes from teeth & mucous membranes of mouth o Resp tract: mucus traps organisms, cilia sweep away trapped organisms o Stomach: acid kills organisms o Bladder: urine washes microbes from urethra - Production of several protective chemicals SECOND LINE OF DEFENSE – NON SPECIFIC DEFENSIVE CELLS & PROTEINS, INFLAMMATION, FEVER - Attack any foreign organism/molecule/cancer cell inside body - 2 line of defense = internal cellular & chemical defenses are activated - Defensive cells (phagocytes) o Engulf pathogens, damaged tissue, dead cells via phagocytosis o E.g. neutrophils – arrive @ site of attack and begins consume of pathogens  Monocytes leave vessels of circulatory, enters tissue fluids, become macrophages  Eosinophils – attack pathogens too large for phagocytosis (parasitic worms) o Natural killer cells (NK)  Roam body searching for abnormal cells  Prime target = cancerous cells, cells infected with virus  Creates pores in abnormal cell so that it leaks away - Defensive proteins o Interferons – slow viral reproduction  Attract macrophages/NK cells  Protect cells that are not yet infected (all strains) o Complement system – assists other defensive mechanisms  Group of 20 proteins whose activities enhance body’s defense mechanisms  Destruction of pathogen  Directly punches holes in target cell’s membrane o Cell cannot maintain constant internal enviro  Proteins make membrane leaky == bursting  Enhancement of phagocytosis  Proteins attract macrophages & neutrophils to site of infection to remove foreign cells  Complement proteins binds to surface of microbe, making it easier for macrophages/neutrophils to get a grip on intruder  Stimulation of inflammation  Cause blood vessels to widen & become more permeable o Increase blood flow to area & access to wbc o Inflammatory response  Destroys invaders & helps repair and restore damaged tissue  4 cardinal signs =  Redness: blood vessels dilate (widen) in damaged area to increase blood flow in area o Dilation caused by histamine – released by small mobile connective tissue MAST CELLS  Heat: increased blood flow elevates temp in area of injury o Increase metabolic rate of body cells in regions and speeds healing. Increases activity  Swelling o Injured area swells b/c histamine makes capillaries more permeable/leaker than usual o Fluid seeps into tissues from blood stream bringing with it many beneficial substances o Blood clotting factors enter injured area & begin to wall of region protecting surrounding areas from injury & excessive loss of blood  Seepage increases o2 & nutrient supply  Pain o Excessive fluid leaked into tissue presses on nerves o Soreness from bacterial toxins o Injured cells release pain-causing chemicals (prostaglandins) o Pain causes person to protect area to avoid additional injury o Fever – abnormally high body temperature  Caused by pyrogens (raise thermostat/hypothalamus in brain)  Slows growth of bacteria & stimulating body defense response  Fever causes liver/spleen to remove iron from blood (which bacteria need to reproduce)  Increases metabolic rate of body cells – speed up defensive response/repair process THIRD LINE OF DEFENSE: ADAPTIVE IMMUNE RESPONSE - Provides specific responses & memory - Organs of lymphatic system important - Recognize & destroy specific pathogens/foreign molecules - Distinguishing self from nonself o MHC markers (major histocampatibility complex) to distinguish what is part of body and what is not o Antigen: nonself substance/organism that triggers an immune response - Lymphocytes – responsible for specificity & memory of adaptive immune response o B cells + T cells  Both form in bone marrow, B cells mature in bone marrow, T cells mature in thymus gland in heart o Effector cells carry out attack on body – live only for a few days o Memory cells 1. THREAT - Organism w/o MHC evades first 2 lines of defense and enters body 2. DETECTION - Macrophages engulfs, digests in
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