Lesson 7: The Integumentary System The Integument • Largest system of the body o 16% of body weight o 1.5 to 2 m2 in area • Made up of two parts: o Cutaneous membrane (skin) o Accessory structures • Cutaneous Membrane o Two components Outer Epidermis: Superficial epithelium (epithelial tissues) Inner Dermis: Connective tissues • Accessory Structures o Originate in the dermis o Extend through the epidermis to skin surface o Includes: Hair Nails Multicellular exocrine glands • Integumentary system is connected to: o Cardiovascular system – blood vessels in the dermis o Nervous system – sensory receptors for pain, touch, and temperature • Hypodermis (Superficial Fascia or Subcutaneous Layer) o Below the dermis o Loose connective tissue o Location of hypodermic injections • Five functions of the skin: o 1. Protection of underlying tissues and organs o 2. Excretion of salts, water, and organic wastes (glands) o 3. Maintenance of body temperature (insulation and evaporation)o 4. Production of melanin, keratin, vitamin D3, and storage lipids o 5. Detection of touch, pressure, pain, and temperature Epidermis • Composed of stratified squamous epithelium o Avascular, nutrients, and oxygen diffuse from capillaries in the dermis o Dominated by keratinocytes (most abundant type of epithelial calls) Contain large amounts of keratin protein • Thin Skin o Covers most of the body o Has four layers of keratinocytes • Thick Skin o Covers the palms of the hands and soles of the feet o Has five layers keratinocytes• The five strata of keratinocytes in thick skin o From basal lamina free surface (inferior to superior) 1. Stratum basale 2. Stratum spinosum 3. Stratum granulosum 4. Stratum lucidum 5. Stratum corneum Stratum Basale • Lowest layer • Hemidesmosomes o Attaches the stratum basale to basement membrane• Forms a strong bond between epidermis and dermis • Forms epidermal ridges o Basis of fingerprints o Ridge patterns of skin increase surface area and friction, ensuring a secure grip • Dermal papillae (tiny mounds) o Increase the area of basement membrane o Strengthen attachment between epidermis & dermis • Has many basal cells or germinative cells • Specialized cells of stratum basale: o Merkel Cells Found in hairless skin Respond to touch (trigger nervous system) o Melanocytes Contain the pigment melanin Scattered throughout stratum basale Stratum Spinosum • “Spiny layer” • Produced by division of stratum basale • 8-10 layers of keratinocytes bound by desmosomes • Cells shrink until cytoskeletons stick out (spiny) • Continue to divide, increasing thickness of epithelium • Contain dendritic (Langerhans) cells • Active in immune response Stratum Granulosum • “Grainy layer” • Stops dividing, starts producing • Keratin: Tough, fibrous protein that makes up hair and nails • Keratohyalin: Dense granules; cross-link keratin fibers • Cells of the stratum granulosum… o Produce protein fibers o Dehydrate and die o Create tightly interlocked layer of keratin surrounded by keratohyalin Stratum Lucidum • “Clear layer” • Found only in thick skin • Covers stratum granulosum • Cells are flattened, densely packed with keratin, devoid of organelles Stratum Corneum • “Horn layer” • Top layer • Exposed surface of skin (15-30 layers of keratinized cells) • All exposed skin surfaces (except anterior of eyes) undergo cornification (keratinization) o Formations of protective, superficial layers of cells filled with keratin o Cells are dead & linked together by desmosomeso Water resistant (not waterproof) o Shed & replaced every 2 weeks • It takes 15-30 days for a cell to move from stratum basale to stratum corneum o Cells may stay an additional 2 weeks before shedding off • Perspiration occurs by: o Insensible Perspiration: Interstitial fluid lost by evaporation through the stratum corneum Lose about 500 mL (1 pint) of H2O per day o Sensible Perspiration: Water excreted by sweat glands • Dehydration can result… o From damage to stratum corneum Ex) burns & blisters (insensible perspiration) o From immersion in hypertonic solution Ex) Seawater (osmosis) – dangerous for shipwreck survivors • Hydration can also occur through osmosis o Results from immersion in hypotonic solution Ex) freshwater o Causes swelling of epithelial cells (evident on palms & soles) Skin Color • Influenced by two pigments: o Carotene o Melanin • Blood circulation (red blood cells) can affect skin color • Carotene: Orange-yellow pigment o Found in orange vegetables Ex) Carrots, squashes – if too much is consumed, can turn skin orange carotenosis o Accumulates in epidermal cells and fatty tissues of the dermis o Can be converted to vitamin A for maintenance of epithelia & photoreceptor function Lack causes night blindness – nyctalopia • Melanin: Yellow-brown or black pigment o Produced by melanocytes in stratum basale (from the amino acid tyrosine) o Stored in melanosomes – transport vesicles o Transferred to keratinocytes o Albino individuals have melanocytes but lack the ability to produce melanin o Protects skin from sun damage Ultraviolet (UV) Radiation: Causes DNA mutations and burns that lead to cancer and wrinkles • Melanosomes of keratinocytes concentrate around nucleus to protect DNA o Skin color depends on melanin production, not number of melanocytes• Blood flow o Capillaries carrying blood can alter skin color o Oxygenated red blood contributes to skin color Blood vessels dilate from heat skin reddens Blood flow decreases skin pales o Cyanosis: Bluish skin tint caused by severe reduction in blood flow or oxygenation • Illnesses that affect skin color: o Jaundice: Buildup of bile produced by liver; yellow color o Pituitary Tumor: Excess MSH (melanocyte-stimulating hormone) Extremely bronze tan o Addison’s Disease: Disease of the pituitary gland Releases more ACTH (adrenocorticotropic hormone) Similar effect on the skin color as MSH (bronze tan) o Vitiligo: Loss of melanocytes; loss of color Evidence points to autoimmune reaction by antibodies Vitamin D3 Production • Vitamin D3 produced by epidermal cells in the presence of UV
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