HostDef09Rev121_OLS - Host Defenses Part 1 Nonspecific...

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Host Defenses Part 1: Nonspecific Defenses Nonspecific defenses are those defenses that are effective against a wide variety of invading microbes (not targeted against a specific invading microbe) Physical Barriers 1. Skin A. Skin consists of layers of tightly packed epithelial cells: When skin is intact most microbes cannot penetrate through it B. The outer layer of skin consists of dead cells and keratin protein, this offers additional protection since attaching to a dead cell is a “dead end” for most microbes C. Skin is relatively dry (dryness is unfavorable for many microbes) D. Cells are shed continuously which removes any attached microbes 2. Mucous membranes A. Mucous membranes consist of tightly packed epithelial cells that secrete mucus B. Mucous membranes line the respiratory, gastrointestinal, and genitourinary tracts C. Secreted mucus is thick and sticky which traps many microbes D. Cells making up the mucous membranes are all living cells, there is no outer layer of dead (protective) cells E. Mucous membranes inhibit penetration of many microbes, but are not as effective as skin F. Ciliary escalator: Special ciliated mucosal cells found in the respiratory tract: these cells sweep trapped microbes upward (away from the lungs) to the throat where they are eventually swallowed (smoking severely damages the ciliary escalator) 3. Flushing action of body fluids Tissues are washed or “flushed” by the movement of certain body fluids like tears, saliva, and urine 4. Epiglottis The epiglottis is a flap that closes the opening to the “wind pipe” (larynx and trachea) during swallowing. The action of the epiglottis keeps swallowed material out of the lungs 1
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5. Normal microbiota Normal microbiota create “microbial antagonism” where invading microbes are blocked from finding attachment sites or are otherwise adversely affected Chemical Barriers 1. Lysozyme An enzyme found in mucous secretions, tears, sweat, and saliva that kills certain bacteria by destroying their cell walls 2. Acid Acid kills microbes in the stomach, vagina, bladder, and on skin
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HostDef09Rev121_OLS - Host Defenses Part 1 Nonspecific...

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