1/28/15INTEGUMENTARY SYSTEM I IntroductionA. Integument : covering=skin (skin=largest organ of the body) B. Integumentary system = Skin + Exocrine glands + Hair + Nails +associated nerves + associated blood vessels II Layers of the IntegumentA. Epidermis: (epi=on, derma=skin)1. Outer layer2. Composed of keratinized stratified squamous epithelium 3. Avascular4. -Thick skin = 5 layers - Thin skin = 4 layers B. Dermis1. Middle layer2. Composed primarily of dense irregular connective tissue 3. Contains nerve endings, hair follicles(cells that make the hair), & glands4. Dermal papillae (projections of the dermis into the epidermis) C. Subcutaneous layer (= hypodermis; superficial fascia)1. Deepest layer2. Stores fat and anchors upper layers to other tissues 3. Composed of areolar CT and adipose CT III Layers of EpidermisA. Stratum Basale: single layer of columnar/cuboidal cells resting on the basement membrane; cells are very mitotic [stratum means layer] [highly mitotic---place where most mitosis happens]B. Stratum Spinosum: several layers of polygonal-shaped cells with spines. Small degree of mitosis here (looks like the spine=spinylayer] C. Stratum Granulosum: 3-5 layers of flattened cells with visible granules; cells undergo keratinization here (keratinization = the process by which the nucleus shrivels up, cell dies, and cell fillsup with the protein keratin)D. Stratum Lucidum(lucid=clear):2-3 layers of dead, anucleated, keratinized, clear cells; only found in thick skin (where we havecaliced skin) E. Stratum Corneum: 20-30 layers of dead, keratinized, anucleated(nucleus has disrupted) cells (cornified = brittle, hardened); outer cells are constantly shed IV Cells of the Epidermis (4 populations of cells)1. Keratinocytes: most numerous (90%); found in all layers; produce keratin (these are the epithelial cells that are squamous/bricklike/columnar/cuboidal/etc)2. Melanocytes: 2nd most numerous (8%);found only in the stratum basale; produce melanin (comes in several diff forms of proteins---dictates your skin color) ***melanin protects us from ultra violet light (could damage DNA and cause cancer 3. Tactile (Merkel) Cells: 3rd most numerous (1%); found only in the stratum basale; provide information regarding tactile (light touch) sensation 4. Epidermal dendritic (Langerhans) cells: 4th most numerous (<1%);found primarily in the stratum spinosum; phagocyte(defense system)V Layers of the DermisA. Papillary Layer: uppermost; composed of dermal papillae; contains blood vessels; sensory receptors (neurons); portions of the ducts of glands and hair roots B. Reticular Layer: deepest;contains blood vessels;sensory receptors (neruons); secretory portions of glands; hair follicles; ducts of glands VI Epidermal Derivatives (Skin Appendages)A. Hair:1. 3 parts: bulb, root, and shaft2. Arrector pili muscle (pili=hair, arrect=to go up)3. Function: protect from UV light, trauma, and heat loss B. Nails: 1. formed from stratum corneum-made out of keratin 2. Function: protection and grasping C. Exocrine glands: 3 kinds1. Sebaceous glands = Oil (= sebum) glandsa. associated with hair follicles b. Functions: soften the skin & bactericidal 2. Sweat (sudoriferous) glandsa. Eccrinei. found everywhereii. releases perspiration (sweat) –sweat is used for cooling, as water evaporates it starts cooling you b. Apocrinei. axillary and pubic regionsii. Secretes onto hair shaftsiii. Releases an odiferous secretion 3. Ceruminous (cerumen = earwax)a. Modified sweat glandsb. in external auditory canal c. Cerumen is an insect repellant and helps keep the eardrum “soft” (helps lubricate it so its able to move without tearing) Which of the following cells is found only in the stratum basale and is a light touch receptor?a. Keratinocyteb. Fibrocytec. Epidermal dendritic (Langerhans) celld. Tactile (Merkel) cell *****e.