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Week/Lecture 3: Integumentary System.pdf

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BIOL 171

General Functions of Skin protection waterproof temp regulation secretion synthesis detecting sensations appearance General Anatomy largest organ composed of tissue types approx. 2 sq. meters, 1-2 mm thick, 10 lbs epidermis: epithelial tissue dermis: connective, nerve, muscle tissue (small amounts of epithelial tissue) subcutaneous (hypodermis): layer of adipose, areolar tissue, lies deep to skin Epidermis keratinocytes most numerous epidermal cell (90%) produce keratin and lamellar granules coat cells to waterproof melanocytes 8% of epidermal cells produce melanin (brown pigment) Langerhans cells migrate from red bone marrow as white blood cells, into blood to skin involved in immune response to microbes invading the skin Merkel cells + tactile discs + sensory neuron located in deepest layer of epidermis function in sensation of touch lamellar granules Epidermal Cell Layers: stratum basale most important layer b/c closest to blood supply cells in constant mitosis b/c of good supply of oxygen/nutrients from blood (new cells pushed upwards) stratum germinativum stratum spinosum thickest layer in epidermis polyhedral shaped cells with spiny projections to bind cells together 8-10 cells thick barrier to limit movement across skin gives strength, flexibility to skin takes in melanin from nearby melanocytes by phagocytosis stratum granulosum dividing line between dead and alive cells 3-5 layers of dying cells, b/c far away from blood supply clear, flat, cells. flattened keratinocytes undergoing apoptosis (organized death) keratohyalin granules: proteins that link together keratin lamellar granules secrete lipid-rich material between cells to waterproof body keratinocytes die, leave sacs full of keratin stratum lucid seen only in thick skin (palms, soles) 3-5 layers of clear, dead, flat keratinocytes containing much keratin cells have thickened plasma membranes stratum corneum (horny) most superficial layer of skin 25-30 layers of flat, dead cells filled with keratin, surrounded by lipids continuously shed protects underlying tissues from light, heat, water, chemicals, bacteria horny: looks like scales- cells peeling off. Keratinization and Epidermal Growth: 1.Stem cells divide --> keratinocytes 2.Keratinocytes fill with keratin as they are pushed towards the surface 3.4 week life cycle, unless outer layers removed by abrasion 4.Process accelerated by epidermal growth factor (EGF) callouses: constant rubbing on outer layer, stimulates growth of more cells Skin Colour: Melanocytes very sensitive to radiation, but also stimulated by radiation inject the melanin into surrounding epidermal cells if injured by radiation, no longer create melanin Melanin protects keratinocytes from injury by blocking radiation Uv radiation hits keratinocytes nucleus', causes mutations in cells melanin located only on surface of nucleus exposed to radiation Colour determined by genetics abundance of melanocytes colour of melanin produced ability to break down melanin affected by: exposure to UV light (needed to activate Vitamin D-- absorbs calcium to strengthen bones) blood flow to skin (more blood=pinker/redder) blood oxygen saturation presence of abnormal pigments (e.g. bilirubin creates jaundice) Dermis composed
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