Lecture 4 Skin PDF
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Summary
This lecture discusses the structure and functions of the integumentary system, focusing on the skin. It details the layers of the epidermis, including the stratum germinativum, spinosum, granulosum, lucidum, and corneum; and the functions of skin such as protection, temperature regulation, and vitamin D synthesis. The lecture also covers skin color, and common abnormal skin conditions.
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Support & Movement Integument ary System Size of the Integument Largest system of the body: 16% of body weight 1.5 to 2 m2 surface area Components of the Integument Cutaneous membrane (skin) Accessory structures Cutaneous Membrane Structure of the Cutaneous Membrane Outer epidermis: e...
Support & Movement Integument ary System Size of the Integument Largest system of the body: 16% of body weight 1.5 to 2 m2 surface area Components of the Integument Cutaneous membrane (skin) Accessory structures Cutaneous Membrane Structure of the Cutaneous Membrane Outer epidermis: epithelium Inner dermis: connective tissue Accessory Structures EXOCRINE GL ANDS Derived from embryonic epidermis HAIR MAMMARY GLANDS CERUMINOUS GLANDS NAILS Located in dermis Project through the skin surface Blood & Nerve Supply Epidermis Is Avascular Blood supply: blood vessels in the dermis Nerve supply: sensory receptors for pain, temperature, touch, and pressure Functions of the Integument Protects underlying tissues and organs Maintains body temperature (insulation and evaporation) Excretes water, salts, and organic wastes Synthesizes vitamin D3 Stores lipids Sensation: pain – temperature – touch – pressure Structure of the Cutaneous Membrane Epidermis Stratified squamous epithelium Avascular: nutrients and O2 diffuse from capillaries in the dermis Keratinocytes: most abundant cells in the epidermis organized in layers contain large amounts of keratin Types of Skin Thin Skin Thick Skin Location Most of the Palms and # of Layers body Soles Stratum 4 5 lucidum Absent Present Layers (Strata) of the Epidermis 5 strata of keratinocytes in thick skin from basal lamina to free surface: ̶stratum germinativum ̶stratum spinosum 5 ̶stratum granulosum 4 3 ̶stratum lucidum 2 ̶stratum corneum 1 Layers (Strata) of the Epidermis o stratu m N m l uc i d u 4 strata of keratinocytes in thin skin from basal lamina to free surface: ̶stratum germinativum 4 ̶stratum spinosum 3 ̶stratum granulosum 2 ̶stratum corneum 1 Stratum Germinativum (Basale) The “germinative layer” Most basal layer 1–3 layers of cells Many germinative (stem - basal) cells Attached to basement membrane by hemidesmosomes Cells of Stratum Germinativum Basal (germinative) keratinocytes: ̶dominant cells ̶replace lost cells Merkel cells: ̶found in hairless skin ̶touch receptors Melanocytes: Melanocytes: CT cells migrate ̶produce melanin pigment from the dermis to the stratum germinativum of the epidermis Stratum Spinosum The “spiny layer” Produced by division of stratum germinativum 8–10 layers of keratinocytes bound by desmosomes Cells of Stratum Spinosum Keratinocytes: ̶some continue to divide, increasing thickness of epithelium ̶they shrink until cytoskeleton sticks out (spiny) Langerhans cell Langerhans cells: ̶dendritic cells ̶skin macrophages ̶active in immune response (antigen-presenting cells) Stratum Granulosum The “grainy layer” 3–5 layers of keratinocytes Cells stop dividing & start producing: ̶keratin: tough, fibrous protein covers the epidermis makes up hair and nails ̶keratohyalin: dense protein granules cross-link keratin fibers Cells of Stratum Granulosum Keratinocytes: do not divide produce protein fibers nuclei and organelles disintegrate dehydrate and die create tightly interlocked layer of keratin surrounded by keratohyalin Stratum Lucidum The “clear layer” ONLY in thick skin 3–5 layers of keratinocytes Keratinocytes: dead flat dense filled with keratin Stratum Corneum The “horny layer” Exposed surface of skin 15 to 30 layers of keratinized dead cells Significantly thicker in thick skin Water resistant Sheds and is replaced every 2 weeks Thin skin Thick skin Keratinization (Cornification) Forming a protective layer of dead cells filled with keratin Occurs on all exposed skin surfaces except eyes Structure of the Epidermis i t in Thhick nn Is t kh s t i i r o i n? sk Skin Life Cycle It takes 15–30 days for a Keratinocyte to move from stratum germinativum to stratum corneum i tick sh k IT i c n t khiin h sr o i n? t sk Perspiration Elimination of fluid through skin pores Insensible perspiration: interstitial fluid lost by evaporation through the stratum corneum 500 ml/day Sensible perspiration: water (sweat) excreted by sweat glands variable amount Water Loss Through Skin Dehydration results from: damage to stratum corneum, e.g., burns and blisters (insensible perspiration) immersion in hypertonic solution, e.g., seawater (osmosis) Xerosis = dry skin Water Gain Through Skin Hydration: results from immersion in hypotonic solution, e.g., freshwater (osmosis) causes stretching and wrinkling of skin (washer hands) Normal & Abnormal Skin Colors Skin Color (Complexion) Depends on: pigments: carotene melanin blood circulation: RBCs Carotene Orange-yellow pigment Found in orange vegetables (carrots) Accumulates in epidermal cells and fatty tissues of the dermis Precursor of vitamin A Melanin Brown-black pigment Produced by melanocytes in stratum germinativum Stored in transport vesicles (melanosomes) Transferred to keratinocytes Skin color depends on melanin production, not number of melanocytes Protects skin from sun damage by UV rays Melanocytes: CT cells migrate from the dermis to the stratum germinativum of the epidermis Freckles & Nevi Freckles: small pigmented areas mainly on the face with sun exposure Nevus (mole): benign melanoma Capillaries & Skin Color Hemoglobin pigment in RBCs contributes to skin color: ̶vasodilation red skin ̶vasoconstriction pale skin Pallor: ̶skin and mucous membranes ̶usually associated with anemia (low hemoglobin concentration) Cyanosis Bluish skin discoloration Due to severe hypoxia ( blood O2) Causes: ̶extreme cold ̶cardiovascular disease ̶respiratory disease Common Abnormal Skin Colors Jaundice: ̶yellow color ̶buildup of bilirubin pigment (hyperbilirubinemia) Vitiligo: ̶autoimmune disease ̶loss of melanocytes ̶loss of skin color Skin & Vitamin D Epidermal cells produce cholecalciferol (vitamin D3): requires UV radiation from sunlight Liver and kidneys activate vitamin D (calcitriol) Function: enhances absorption of Ca and P from intestine Vitamin D Deficiency Children: ̶rickets Adults: ̶osteomalacia Malignant Skin Tumors Basal Cell Carcinoma Malignant Melanoma Squamous Cell Carcinoma Epidermal Ridges & Dermal Papillae Strengthen the bond between epidermis and dermis Epidermal ridges: Epidermis Basement membrane ̶formed by stratum germinativum Epidermis ridge ̶fingerprints Dermal papilla Dermal papillae: Dermis ̶project through epidermal ridges ̶increase the area of basal lamina Ridges, Ducts & Fingerprints Pores of sweat gland ducts Epidermal ridge Thick skin SEM × 20 Do identical twins have identical fingerprints? Yes No Do identical twins have identical fingerprints? Yes No Epidermis at a Glance Stratified squamous epithelium Multilayered, flexible, self-repairing barrier Avascular Color depends mainly on melanin pigment Resists abrasion, chemicals, and pathogens Prevents fluid loss Protects from UV radiation Produces vitamin D3