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Unformatted text preview: Chapter 43 The Immune System I. Immunity provides defenses A. External Defenses 1. Skin barrier prevents most microbes from entering body 2. Certain cells produce mucous which traps microbes a. Washing action i Saliva and tears wash away microbes 3. Secretions of the skin and mucous membranes are acidic, preventing microbe colonization 4. Lysozyme- an antimicrobial enzyme which digests the cell wall of many bacteria B. Internal Cellular and Chemical Defenses 1. Phagocytic cells a. Phagocytosis- ingestion of invading microorganisms by phagocytes b. Phagocytes- several types of blood cells i Attach to their prey via surface receptors that bind to structures found on microorganisms but not human cells ii Then engulfs it by forming a vacuole that fuses with a lysosome iii Lysosomes destroy the microbes by poisoning the microbe and then degrading its components c. Some bacteria have defenses so that the macrophages dont engulf them i Outer capsule that surrounds some bacterial cells hide their surface receptors 2. White Blood Cells a. Neutrophils i 60-70% of white blood cells ii Engluf and destroy microbes iii Self-destruct in the process iv Life span only a few days b. Macrophages i Develop from monocytes ii 5% of blood c. Eosinophils i Low phagocytic activity ii Critical to defense against multi-cellular parasitic invaders Instead of engulfing the parasite they discharge destructive enzymes into the parasite to damage it 3. Antimicrobial Proteins a. Complement system i Contain 30 serum proteins ii Inactive in absence of infection iii Activation of the complement leads to lysis (bursting) of the invading cells iv Triggers inflammation 1 b. Interferon i Proteins are secreted when a body cell is infected with a virus. It warns other cells about the presence of this virus, and they produce substances that inhibit viral production. ii Nonspecific defense iii Alpha iv Beta v Gamma- activates macrophages, enhancing their phagocytic ability Defensins- secreted by activated macrophages 4. Inflammatory Response a. Caused by damage to tissue by physical injury or the entry of pathogens b. Histamine is one of the most active chemicals i Stores in mast cells which are found in the connective tissue c. When injured, mast cells release histamine i Dialation ii Increased permeability of nearby capillaries d. Activated macrophages discharge signals increasing blood flow to injured site i Causes redness and heat e. Blood clotting begins the repair process and helps block spread of microbes f. Increased blood flow allows more neutrophils and macrophages to move to the injured site g. Chemokines- proteins that direct the migration of phagocytes and signal them to increase production of microbe-killing compounds Chemical signals released by activated macrophages and mast cells at the injury site. It causes nearby capillaries to widen and become more permeable....
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