Skin

Skin

1. Structure

   • I. Epidermis (top of skin)
     • mostly made of stratified squamous epithelia tissue
     • CELL types: 1. keratinocytes-keratin protein production (toughness, waterproofing), 2. melanocytes -melanin production-protects from UV radiation, 3. Langerhans cells-macrophages cells, 4. Merkel cells-touch detection.
       • Note: skin colour is due to protein MALANIN. The darkness of skin depends on the amount and type of pigment produced by melanocytes rather than the numbers of melanocytes. CAROTENE causes the yellow-orange colour. HAEMOGLOBIN causes the skin look pink-red dependinmg on the amount and and oxygen content of blood
     • LAYERS: (1) Stratum Basale, (2)Stratum Spinosum, (3) Statum Granulosum, (4) Stratum Corneum, (5) Sratum Lucidium
   • II. Dermis
     • mostly Connective tissue with collagen and elstic fibres
     • Contains nerves, hair follicles, blood vessels
     • 2 main regions: (1) Papillary region (top), (2) Reticular region (deeper)
   • III. Hypodermis (very bottom of skin) (subcutaneaus layer/superficial fascia)
     • Contains large amount od ADIPOSE and AREOLAR tissues
     • anchors the skin to muscles
     • insulates
     • shock absorber

2. Skin appendages: oil glands, sweat glands, hair & hair follicles, nails

3. Function of SKIN

   • 1. Protection as chemical (e.g. melanin-UV radiation protection), physical (e.g. glycolipids prevent water soluble substances to get through skin), or biological (e.g. DNA converts harmfull UV radiation ino harmless heat)barriers
   • 2. Body temperature regulation: cools body with perspiration (sensible or insensible); shaking warms up body)
   • 3. Cutaneous sensation: skin receptors respond to pain, touch, temperature, and pressure
   • 4. Metabolic functions: synthesises vitamin D PRECURSOR, important for increased CALCIUM absorption from food
   • 5. Blood reserviour: the extensive blood vessels in the skin allow the storage of blood, and cab be directed to where it is needed. e.g. if we are cold, blood flows to core: brain, heart etc.-we look pale/ white
   • 6. Excretion: the body eliminates a LIMITED amount of nitrogenous substances (ammonia, urea) in sweat, although most of these is secreted in urine. We get Nitrogen from protein, is toxic for body, thus needs to be secreted.

4. Tissue repair

   • 1. Regeneration: new cell is identical to damaged cells
   • 2. Replacement: new tissue develops with scarring and loss of function
     • Burns: 1st, 2nd, 3rd degree burns and their differntiation