mbbs 1st prof exam

4. Skin and Its Tissues Skin Functions 1. Protection - Physical barrier a. from water loss b. from injury c. from chemicals and microorganisms - Chemical barrier a. pH or 5-6 b. prevents microorganism growth - Biological barrier a. Langerhan’s cells (epidermis) b. Macrophages and mast cells (dermis) 2. Excretion (minimal, most through kidneys!) - urea - uric acid 3. Regulation of body temperature -

5. Skin and Its Tissues Skin Functions 4. Cutaneous Sensation - Light touch detection = Meissner's Corpuscle's a. egg-shaped; b. located in dermal papillae; c. populate areas in the fingertips, palms, soles, eyelids, tip of tongue, nipples, clitoris, tip of penis. - Pressure detection = Pacinian Corpuscle's a. onion-shaped; b. located in deep dermis and subcutaneous regions - Free nerve endings a. respond to temperature changes or to factors that can damage tissues b. extend into epidermis

6. Skin and Its Tissues Skin Functions 5. Vitamin D Synthesis - UV rays in sunlight activate its synthesis; - Vitamin D is required for bone homeostasis. 6. Blood Reservoir - The dermis houses about 10% of the body's blood vessels. - Skin only requires 1-2% of the body’s blood 7. Immunity - Langerhan’s cells (macrophages); - interact with T-helper cells in immune responses.

7. Skin and Its Tissues

9. Skin and Its Tissues Hair Follicles 1. Epidermal cells that form a tube-like structure that extends into the dermis 2. Three parts: 1. Hair shaft 2. Hair root 3. Hair papilla 3. Cells that move upward and away from the nutrient supply ( papilla ) become keratinized and die 3. Pigments include: eumelanin – brownish- black pheomelanin – reddish- yellow 4. Arrector Pili Muscle = a bundle of smooth muscle associated with every hair follicle. a. causes hair to stand on end ("goose bumps") when frightened or cold.

10. Skin and Its Tissues Nails 1. Epithelium undergoing keratinization 2. Three parts: 1. Nail plate 2. Nail bed 3. Lunula 3. Functions: a. manipulation; b. protection of digit ends.

11. Skin and Its Tissues Sebaceous Glands 1. holocrine gland (simple cuboidal epithelium) 2. associated with every hair follicle 3. Secretion = sebum (oil) a. fat b. cellular material 4. Sebum is secreted into hair follicle 5. Function: Sebum keeps skin & hair soft, pliable and virtually waterproof. .

12. Skin and Its Tissues Sweat Glands 1. Two types (based on glandular secretion) A. Eccrine glands - Structure: 1. coil in deep dermis 2. duct in dermis 3. pore at surface - Characteristics: 1. respond to elevated temperature / exercise 2. no odor in secretion 3. function throughout life 4. not associated with hair follicles 5. Location: forehead neck back - Secretion (merocrine) = water plus 1. salts and 2. wastes (urea and uric acid)

13. Skin and Its Tissues

14. Skin and Its Tissues Sweat Glands or Sudoriferous Glands B. Apocrine glands - Structure: ducts terminate into hair follicles - Characteristics: 1. respond to stress / emotions 2. odor in secretion 3. begin to function at puberty & continue through life 4. associated with hair follicles 5. Location: axillary regions and groin - Secretion (apocrine) = water above plus 1. oil and 2. cellular debris 3. Modified Sweet Glands 1. Ceruminous glands = external ear; secretion = earwax; 2. Mammary glands = breasts; milk.

15. Skin and Its Tissues Subcutaneous Layer (hypodermis) 1. beneath skin 2. Structure = adipose tissue & blood vessels 3. Function = insulation

17. Regulation of Body Temperature

23. Mechanisms of Body Temperature Regulation

27. Hypothermia – low body temperature a. very dangerous if core body temperature drops below 94 F b. limbs can withstand about 65 F because they contain no vital organs