2. Integument(Skin) Integument is nothing but the skin. Integument(=to cover in latin Skin and its appendages are the largest organ of the body Functions: 1. Protection 2. Heat regulation 3. Sensation 4. Synthesis and storage of Vit D

3. Integumentary system Skin along with the exocrine gland(sebaceous gland Hair Nails Associated blood vessels and Associated nerves Comprise integumentary system

4. Skin Superficial epidermis middle dermis Deep hypodermis(superficial fascia)

5. Epidermis Superficial layer composed of keratinized stratified squamous epithelium Avascular with no blood vessels or lymphatics Has basal cells which has regenerative capacity Thick skin has 5 layers of cells Thin skin has 4 layers of skin

6. Dermis Middle layer composed of Dense irregular connective tissue Contains nerve endings,hair follicles, and glands They nourish the avascular epidermis Contains dermal papillae(projections of dermis into epidermis)

7. Langer(incision or tension) lines in skin They are the direction in which the most collagen fibres run in any particular location in the skin. Incision should be made parallel to the direction to avoid minimal scarring.

8. Hypodermis Deepest layer Stores fat and anchors upper layers to other tissues Composed of areolar and adipose connectieve tissue

9. Epidermal layers From base to top Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum

10. Stratum basale Single layer of columnar or cuboidal cells resting on basement membrane The epidermis is renewed every 15-30 days; proliferative activity takes place in this layer; cells are very mitotic

11. Stratum spinosum several layers of polygonal shaped cells with spines. Spines are nothing but keratin filaments. It resists the effects of abrasion and the layer is thicker in thick skin which is subjected to continuous friction and pressure(eg: soles and palms)

12. Stratum granulosum 3-5 layers of flattened polygonal cells with visible granules Cells undergo keratinization which is a process in which nucleus shivels up, cells dies, and cell fills up with protein keratin This layer acts as a barrier to penetration by foreign materials and provides sealing effect

13. Stratum lucidum 2-3 layers of dead, anucleated, clear cells. Only found in thick skin Stratum Corneum 20-30 layers of dead, anucleated cells. They are cornified( brittle, hardened). These outer cells are constantly shed

14. Epidermal cells Keratinocytes: most numerous(90%);found in all layers; produces keratin which provides the protective barrier mechanically as well as immunologically Melanocytes: 2 nd most numerous(8%);found in stratum basale;produces melanin which is a photoprotector

15. Epidermal cells Merkel cells: 3 rd numerous(1%) found in stratum basale;provides tactile(light touch) sensation Langerhans cells: <1% found in stratum spinosum; phagocytic action

16. Dermal layers Pappillary Layer: uppermost; composed of dermal papillae; contatains blood vessels, sensory receptors, ducts of glands; and hair shafts Reticular Layer: deepest;contains blood vessels; sensory recptors(neurons); secretory poertions of glands and hair follicles

17. Epidermal derivatives(skin appendages) Hair : contains bulb, root and shaft ; associated with arrector pili muscle; functions to protect UV light, trauma, and heat loss Nails : formed from stratum corneum ; functions in protection and grasping Exocrine Glands: 1.Sebaceous glands 2.Sweat (sudoriferous) glands 3.Ceruminous

18. Exocrine glands in skin Sebaceous glands(sebum=oil):associated with hair follicles and functions in lubrication and bactericidal Sweat(sudoriferous) glands:  appocrine: in axiallary and pubic regions, secreates onto hair shafts and release an odiferous secretion  Eccrine : found everywhere, funtioning to release perspiration  Ceruminous: modified sweat glands ; found in external auditory canal; cerumen is an insect repellent and a water proofing agent