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The First Line of Defense The first line of defense is largely physical that prevents pathogens from entering our tissues. Both the skin and the mucous membranes that line the respiratory and digestive systems function as effective physical barriers to invading pathogens. A. THE SKIN · Made up of a layer of dead cells, if intact can prevent pathogens from entering the living tissues beneath it. · Minor scrapes/cuts in the skin can be repaired with blood clots but severe puncture wounds can provide pathogens access to deeper tissues. · Chemical defenses such as acidic secretions and lysoszyme (antimicrobial enzyme secreted in tears, saliva, mucous secretions, perspiration) destroy foreign organisms. B. MUCOUS MEMBRANES · Pathogens or foreign debris get “stuck” in layers of mucous lining the respiratory and digestive tracts and cilia move these pathogens/debris out of the lungs. · Microbes that enter the stomach are destroyed by acidic secretions and protein digestive enzymes found there. The Second Line of Defense If a pathogen enters the body tissues a second line of defense targets and destroys the pathogen using both cellular and chemical tools. Cellular defense mechanisms involve the action of LEUKOCYTES or white blood cells.
Approximate Word count = 754
Approximate Pages = 3
(250 words per page double spaced)
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