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HUMAN ANATOMY & PHYSIOLOGY Skin Standard 3 Describe the structure of skin, including the 3 main layers… “Keeps your insides in.” Protect deeper tissues from infection and some toxins. Thermoregulation – control of body temperature. Synthesis of the active form of Vitamin D (the “sunshine vitamin” – a steroid vitamin) Social and cosmetic implications Epidermis • avascular • no nerve supply • mainly stratified squamous epithelium • often keratinized for protection and waterproofing • basement membrane border between epidermis and dermis • Skin grows from the bottom (basal layer) up. • As the new cells age they rise up and begin to die. They eventually fall off and are replaced by a new generation of cells produced in the basal layer. • As the cells age, the proportion of stringy, waterproofing keratin protein increases. In the outer layer, all that remains is the keratin of dead skin cells. They fall off (scales, dandruff, etc.) • 5 layers: Big Sexy Girls Love Cake Dermis • vascular; good supply of blood vessels • Good nerve supply; painful if damaged • mainly dense irregular connective tissue. • Mainly dense irregular connective tissue. • The “hide” of leather. • Rich in blood and nerve supply. • Rich in collagen and elastin fibers. • Tough but pliable. • Irregular surface – dermal pegs. Hypodermis (Subcutaneous) • Vascular; less blood supply than dermis • rich in adipose tissue • anchors skin to deeper structures, especially muscle Draw and Label a diagram of the skin, including accessory organs. (Incl. sebaceous, eccrine sweat, apocrine sweat) Draw and label a diagram of a nail. Draw and label a diagram of hair. Of these functions of the skin, describe the mechanism/ physiology… Provides a protective barrier against mechanical, thermal and physical injury and noxious agents. Keratin (strands of tough, fibrous, waterproof protein fibers) fill the outer layer of the epidermis. Prevents loss of moisture. Keratin, as well as the ability to change blood flow to the peripheral blood vessels. Reduces the harmful effects of UV radiation. Melanin absorbs UV radiation that might otherwise cause damage to the DNA of cells. Acts as a sensory organ. The dermis contains many nerve endings that sense touch, pressure, pain, temperature, etc. Helps regulate temperature control. Heat is a product of cellular metabolism, especially in the skeletal/cardiac muscles, and the major organs (like the liver) radiation – heat transfer by infrared heat rays. Can occur in a vacuum. convection – heat transfer by contact with a fluid medium (gas, liquid) conduction – heat transfer by contact with a solid medium. Plays a role in immunological surveillance. The skin acts as a barrier, a kind of sheath, made of several layers of cells and their related glands. The skin is a dynamic organ (constantly changing) that contains different cells which contains elements of the innate/ and the adaptive immune system which are activated when the tissue is under attack by invading pathogens. Shortly after infection, the immune adaptive response is induced by dendritic cells (Langerhans cells) present in the epidermis; they are responsible to capture, process, and present the antigens to T lymphocytes in local lymphoid organs. As result, T lymphocytes express the CLA molecule. Lymphocytes move to the epidermis where they reside as a memory T cells, they will thus be activated and will trigger inflammatory response. Improper regulation of these mechanisms is associated with inflammatory diseases of the skin. No need to memorize this diagram… but take a look at all the stuff you didn’t know your skin could do! Synthesizes vitamin D3 (cholecalciferol). Vitamin D from the diet or dermal synthesis from sunlight is biologically inactive; activation requires enzymatic conversion (hydroxylation) in the liver and kidney. Evidence indicates the synthesis of vitamin D from sun exposure is regulated by a negative feedback loop that prevents toxicity, Vitamin D has a significant role in calcium homeostasis and metabolism. Its discovery was due to effort to find the dietary substance lacking in rickets (the childhood form of osteomalacia). Has cosmetic, social and sexual associations. I feel pretty. Oh so pretty.
