1. Ms. Bowman

2.  Covers the entire body  Surface area of 1.2 to 2.2 square meters  9-11 lb  Accounts for about 7% of total body weight in average adult  Varies in thickness from 1.5 to 4.0 milimeters

3.  Characteristics  Waterproof  Stretchable  Repairs itself  Functions  Protection  Body temperature regulation  Cutaneous sensation  Metabolic functions  Blood reservoir  Excretion

4.  2 distinct regions  Epidermis  Composed of epithelial cells  Outermost protective shield  Dermis  Makes up the bulk of the skin  Tough, leathery layer  Composed of fibrous connective tissue  Vascularized

5.  Subcutaneous tissue deep to the skin  Not technically part of the skin  Shares some of the protective functions of skin  Functions  Stores fat  Anchors skin to underlying structures  Acts as a shock absorber  Insulator

6.  Keratinocytes  Produce keratin (fribrous protein that gives epidermis its protective properties  Undergo continuous mitosis  Pushed upward as new cells are formed  When they reach the top, they are dead  Millions rub off everyday; new epidermis every 25- 45 days

7.  Melanocytes  Spider-shaped epithelial cells that synthesize melanin (pigment)  Melanin protects the nucleus of keratinocytes from the damaging effects of UV radiation from sunlight

8.  Langerhan’s Cells  Arise from bone marrow  Phagocytes that ingest foreign substances  Activates immune system

9.  Merkel Cells  Associated with a sensory nerve ending  Functions as a sensory receptor

10.  Strong, flexible  Binds entire body together  Richly supplied with nerve fibers, blood vessels, and lymphatic vessels  Hair follicles, oil glands, sweat glands reside here

11.  Sweat (Sudoriferous) Glands-  3 million per person  Excrete sweat  Sebaceous (Oil) Glands-  Secrete oily secretion called sebum  Sebum softens and lubricates hair and skin

12.  Hairs and Hair Follicles  Hair helps to keep mammals warm  Main function is to sense insects on the skin before they bite or sting  On head, guards against physical trauma, heat loss, and sunlight  Eyelashes shield eyes  Nose hairs filter large particles from air we inhale

13.  Nails  Forms a clear protective covering on the dorsal surface of the distal part of a finger or toe  Useful as tools to help pick up small objects and scratch an itch