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Integumentary system major components
- The cutaneous membrane (skin)
- Accessory structures
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The cutaneous membrane (skin)
includes epidermis, dermis, and hypodermis (subcutaneous) layers
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Accessory structures
includes hair, nails, and multicellular exocrine glands
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Functions of skin and subcutaneous tissue
- protection (prevents loss of body fluids, inhibits invasion of bacteria, and filters out UV light rays; basically keeps insides in and outside out)
- excretion (sweat glands allow for perspiration and loss of water, salt, urea)
- thermal regulation
- storage of nutrients - lipids
- synthesis of vitamin D3 (sunshine)
- perception of the environment via sensory receptors (Pacinian corpuscles - detects deep pressure in reticular layer of dermis; Meissner's corpuscle - detects pressure/light touch in dermal papilla)
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The epidermis
- outer layer of skin
- stratified squamous epithelium with keratin - these epithelial cells are also called keratinocytes
- made up of 5 layers
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Layers of epidermis
- Stratum germinativum
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Stratum corneum
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Stratum germinativum (stratum basale)
- contain the basal (stem) cells that constantly divide giving rise to keratinocytes
- contains melanocytes providing brown/black pigment to skin
- unique pattern of epidermal ridges formed from underlying dermal papilla = fingerprints
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Stratum spinosum
- fourth layer
- spiney shaped cells derived from division of basal cells
- Langerhan cells = macrophage type immune cells
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Stratum granulosum
- third layer
- production of keratin and keratohyalin granules occur eventually killing cell
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Stratum lucidum
- second layer - lighter layer, like translucent
- glassy layer of flattened cels seen in the thick skin of the palms and soles
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Stratum corneum
- top layer
- consists of tightly packed dead keratinocytes full of keratin
- takes about 15-30 days for cells to move from basal layer to this layer
- take about 2 weeks for cells in this layer to be shed
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Thin skin vs. thick skin
- thin skin: less stratum corneum and hair
- thick skin: more stratum corneum and no hair
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The Dermis
- Middle layer of skin
- composed of papillary and reticular layers
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Papillary Layer of Dermis
- has dermal papilla that project into epidermis giving rise to epidermal ridges - fingerprints!
- contains blood vessels and nerves that supply surface of skin
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Reticular Layer of Dermis
- composed of dense irregular connective tissue
- bundles of collagen fibers extend into reticular layer and subcutaneous layer
- all other cells of connective tissue proper also located here
- effects of aging, hormones, and UV rays reduce amount of elastin causing "wrinkles"
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Hypodermis (subcutaneous layer)
- consists of loose (areolar) and adipose connective tissue and contains large arteries and veins
- hypodermic needles used for subcutaneous injections of drugs
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