Lecture 4 Skin PDF

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