Innate Immunity: Physical and Chemical Barriers
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Innate immunity's first line of defense comprises physical and chemical barriers — skin, mucus, stomach acid, antimicrobial secretions — blocking pathogens before an internal response is needed.
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Stomach acid's low pH, per Bio 2775, destroys many ingested pathogens before the intestine.
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These barriers act nonspecifically, unlike the adaptive response covered later in this chapter.