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Skin - lowermost layer of epidermis single cell layer thick...

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Skin (Integumentary System) considered an organ or an organ system body’s largest organ organ of greatest surface area:15-20 sq ft. (1.5-2 m 2 ) General Functions: 1. protection mechanical chemical bacterial UV desiccation 2. temperature homeostasis >temp sweat glands, flushing <temp arrector pili, pale 3. excretion sweat glands release: water, salts, ammonia oil glands release: lipids, acids 4. sensation touch (light touch, wind, etc) pressure heat cold pain 5. synthesis vitamin D precursor passes through capillaries in skin and light converts it to vitamin D 6. nonverbal communication eg. humans and other primates have much more expressive faces than other animals Layers of Skin:
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epidermis dermis hypoderms Human Anatomy & Physiology: Integumentary System, Lecture Notes, Ziser, 2005 2 Epidermis stratified squamous epithelium upper layers dead, filled with keratin (waxy protein) lower layers living cells replaced every 35-45 days subdivided into 5 identifiable layers: a. stratum basale
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Unformatted text preview: lowermost layer of epidermis single cell layer thick only cells that get adequate nutrition and oxygen by diffusion from tissues below actively dividing cells bordered below by basement membrane b. stratum spinosum several layers thick less mitosis flattened, irregular, spinelike projections [basale + spinosum = stratum germinativum ‡ growing layers] c. stratum granulosum very thin; 2-3 cell layers thick as cells move up from s. basale they die & get flatter and thinner keratinization begins here d. stratum lucidum thin translucent band only found in thick areas of epidermis: soles of feet palms of hand e. stratum corneum thickest of all layers; 3/4 th ‘s the thickness of epidermis 20-30 cell layers thick dead cells completely filled with keratin water resistant main protection against biological and chemical assault takes keratinocytes 30-40 days from their formation in s basale until they flake off of the s corneum...
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