Skin Anatomy PDF

The Anatomy of Skin and Associated Structures Skin is the largest human organ – Epidermis is 0.1 mm thick – Numerous structures embedded in tissue layers Blood vessels Nerves, Mechanoreceptors (nerve endings) Sweat glands Hair follicles Oil gl...

The Anatomy of Skin and Associated Structures Skin is the largest human organ – Epidermis is 0.1 mm thick – Numerous structures embedded in tissue layers Blood vessels Nerves, Mechanoreceptors (nerve endings) Sweat glands Hair follicles Oil glands  The Anatomy of Skin and Associated Structures Skin is composed of two layers of tissue - Outermost epidermis Composed of epithelial cells Rests on a basement membrane - Dermis lies beneath epidermis  Epidermis Keratinized stratified squamous epi. Cells of epidermis: Keratinocytes – produce fibrous protein keratin Melanocytes o 10-25% of cells in lower epidermis o Produce pigment melanin Epidermal dendritic (Langerhans) cells – macrophages that help activate immune system Tactile (Merkel) cells – Touch receptors  Epidermis The epidermis forms a barrier deep to superficial – Five layers 1. Basal cells – rest on the basement membrane and form the stratum basale (basal layer) a. Also contains melanocytes (pigment-producing cells) b. Single row of stem cells 2. Stratum spinosum (prickly layer) a. Contain cuboidal cells joined together by desmosomes b. As they push to the surface they acquire keratin and are now called keratinocytes. Epidermis 5. Stratum corneum (Horny Layer) a. 20-30 rows of dead, flat, keratinized membranous scas b. Waterproof c. Repels environmental agents d. Does not support microbe growth e. When shed, carry away microbes and other hazards  Structures in the Dermis Cell types in the dermis: o Fibroblast: produces collagen and elastin fibers o Macrophages o Dendritic cells Precapillary sphincters Nerves The Dermis - flexible and strong connective tissue - elastic, reticular and collagen fibers - cells: fibroblasts, macrophages (WBC), mast cells (histamine). - nerves, blood and lymphatic vessels - oil and sweat glands originate - two layers: papillary and reticular  Dermis 1- Papillary layer: - loose connective tissue with nipple like surface projection called dermal papilla. Collagen and elastic fibers - capillaries - contain pain receptors - contain touch receptors (Meissner’s corpuscles) - dermal ridges- epidermal ridges- pattern called fingerprints  Dermis 2- Reticular layer: - dense irregular c.t. ~80% of the thickness of dermis - collagen fibers offer strength and resiliency - holds water - dermal tearing causes stretch marks. Skin color: attributed to melanin, hemoglobin and carotene. Race is determined by amount of melanin not # of melanocytes. Melanocytes and Pigmentation Local accumulation of melanin will result in freckles and pigmented moles. Melanin is made through interaction with tyrosinase present in melanocytes UV light stimulates melanin production. Excessive UV light can damage DNA and cause solar elastosis (elastin fibers clump) Carotene is formed from Vit. A and deposits in stratum corneum and imparts an orange tone to skin  Remember This The varying shades of brownness of skin depend on the amount of melanin pigment produced by melanocytes in the epidermis.  Appendages of the Skin Derivatives of the epidermis Sweat glands Oil glands Hairs and hair follicles Nails  Sweat Glands 1. Eccrine (merocrine) sweat glands – abundant on palms, soles, and forehead Sweat: 99% water, NaCl, vitamin C, antibodies, dermcidin, metabolic wastes Ducts connect to pores Function in thermoregulation 2. Apocrine sweat glands – confined to axillary and anogenital areas Sebum: sweat + fatty substances and proteins Ducts connect to hair follicles Functional from puberty onward Specialized apocrine glands o Ceruminous glands – in external ear canal; secrete cerumen o Mammary glands  Sebaceous Glands Widely distribute Most develop from hair follicles Become active at puberty Sebum o Oily holocrine secretion o Bactericidal o Softens hair and skins  Review a. Dandruff is caused by excessive shedding of cells from the outer skin layers of the scalp. Thus, dandruff is composed of cells from which epidermal layer? b. Name two pigments contained in the epidermis c. Why does exposure to sunlight or sunlamps darken skin? d. Why does the skin of a fair-skinned person appear red during exercise in hot weather? Burns Skin Functions Affected by Burns Fluid and Electrolyte Balance. Even areas with partial- thickness burns lose their effectiveness as barriers to fluid and electrolyte losses. In full-thickness burns, the rate of fluid loss through the skin may reach five times the normal level. Thermoregulation. Increased fluid loss means increased evaporative cooling. As a result, more energy must be expended to keep body temperature within acceptable limits. Protection from Infection. The dampness of the epidermal surface, resulting from uncontrolled fluid loss, encourages bacterial growth. If the skin is broken, infection is likely. Widespread bacterial infection, or sepsis (sepsis, rotting), is the leading cause of death in burn victims.  Function of the Skin Basic function of skin is to keep the inside in and the outside out: Protection Retains Body heat Body water Keeps out water, bacteria, chemicals, and other threats Helps regulate body temperature Senses danger Protects against force Synthesizes cholecalciferol (vitamin D) Temperature Regulation  The Functions of Skin (Review) True of false? Blood vessel dilation delivers warm blood to the body surface for cooling. Hair Structure  Hair Structure o Shaft Superficial portion o Root Below the surface o Cuticle Outermost layer of hair o Hair develops in follicles Downward continuation of epidermis  Functions of Hair o Protection o Thermoregulation o Sensory o Minor role in humans  Growth of Hair o At the base of the follicle, hair papilla Contains blood vessels and nerves o Nourishes hair o Bulb Contains matrix – epithelial cells responsible for growth o Contains melanocytes  Arrector Pili o Smooth muscle attaches to follicle o Raises hairs o Response to fright or cold o Function?  Nail Structure o Nail body o Free edge o Nail root Matrix oLunula (moon) Nail Structure  Effects of Aging on the Skin Fewer Melanocytes Drier Epidermis Thinning Epidermis Diminished Immune Response Thinning Dermis Decreased Prespiration Altered Hair and Fat Distribution Fewer Active Follicles Slower Skin Repair Reduced Blood Supply  Recommended Reading McConnell, T. H. & Hull, K. L. (2011). Human form and function: Essentials of anatomy& physiology. Philadelphia: Wolters Kluwer, Lippincott Williams & Wilkins. Shier, D., Lewis, R. & Butler, J. (2002). Hole’s human anatomy & physiology. New York: McGraw Hill. Tortora, Gerard J. & Derrickson, Bryan H. (2011). Principles of anatomy and physiology. Somerset, New Jersey: John Wiley & Sons.