Protection skin provides protection to body in

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Protection Skin provides protection to body in various waysKeratin protects underlying tissues from microbes, abrasion, heat and chemicals and the tightly interlocked keratinocytes resist invasion by microbes Lipids released by lamellar granules inhibit evaporation of water from skin surface, thus guarding against dehydration Also retard entry of water across skin surface during showers and swimsOily sebum from sebaceous glands keeps skin and hair from drying out and contains bacterial chemicals Acidic pH of perspiration retards growth of some microbesMelanin helps shield against UV damageIntraepithelial macrophages alert immune system in presence of harmful invadersMacrophages in dermis phagocytize bacteria and viruses that manage to bypass intraepidermal macrophages of epidermis
Cutaneous Sensations
Excretion and Absorption Skin normally has small role in excretion and absorptionBesides removing water and heat from body sweat is also the vehicle for excretion of small amounts of salts, carbon dioxide, ammonia and ureaAbsorption of water-soluble substances through skin is negligible, but certain lipid soluble materials do penetrate the skinInclude fat soluble vitamins (ADEK), certain drugs, gases (oxygen and carbon dioxide) Toxic materials can be absorbed through skin - organic solvents, salts of heavy metals Topical steroids are lipid soluble and move easily into papillary region of dermis
Synthesis of Vitamin DSynthesis of vitamin D requires activation of a precursor molecule in skin by UV rays in sunlightEnzymes in liver and kidneys modify the activated molecule, finally producing calcitriol – the most active form of vitamin DCalcitriol = hormone that aids absorption of calcium from foods in GI tract into blood only small amount of exposure to UV light is required for vitamin D synthesis Most cells of immune system have vitamin D receptors and cells active vitamin D in response to infection Vitamin D is believed to enhance phagocytic activity, increase production of antimicrobial substances in phagocytes, regulate immune functions and help reduce inflammation

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