a. Keratinocyteb. Fibrocytec. Epidermal Dendritic Celld. Tactile Celle. MelanocyteINTEGUMENTARY SYSTEMI IntroductionA. Integument = covering = skin (largest organ of the body)B. Integumentary system = Skin + Exocrine glands + Hair + Nails + associated nerves + associated blood vesselsII Layers of the IntegumentA. Epidermis: (epi = on, derma = skin)1. Outer layer2. Composed of Keratinized Stratified Squamous epithelium3. Avascular4. Thick skin = 5 layers Thin skin = 4 layersB. Dermis1. Middle layer2. Composed of dense irregular and areolar connective tissues3. Contains nerve endings, hair follicles, & glands4. Dermal papillae (projections of the dermis into the epidermis)Subcutaneous layer (= hypodermis; superficial fascia) not considered part of the integument.• Below dermis• Stores. fat and anchors upper layers to other tissues• Composed of areolar CT and adipose CTIII Layers of EpidermisA. Stratum Basale: single layer of columnar/cuboidal cells resting on the basement membrane; cells are very mitoticB. Stratum Spinosum: several layers of polygonal-shaped cells with spines. Small degree of mitosis hereC. 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 fills up with the protein keratin)D. Stratum Lucidum: 2-3 layers of dead, anucleated, keratinized, clear cells;only found in thick skinE. Stratum Corneum: 20-30 layers of dead, keratinized, anucleated cells (cornified = brittle, hardened); outer cells are constantly shedIV Cells of the Epidermis1. Keratinocytes: most numerous; found in all layers; produce keratin2. Melanocytes: 2nd most numerous; found in the stratum basal with processes extending into the stratum spinous; produce melanin3. Tactile Cells: 3rd most numerous; found only in the stratum basale; provide information regarding tactile (light touch) sensation4. Epidermal Dendritic Cells: 4th most numerous; found primarily in the stratum spinous; phagocyteV Layers of the DermisA. Papillary Layer: uppermost; composed of areolar C.T. and dermal papillae; contains blood vessels; sensory receptors (neurons); portions of the ducts of glands and hair roots.B. Reticular Layer: deepest; composed of primarily dense irregular C.T., contains blood vessels; sensory receptors (neurons); secretory portions of glands; hair follicles; ducts of glandsVI Epidermal Derivatives (Skin Appendages)A. Hair:1. 3 parts: bulb, root, and shaft2. Arrector pili muscle3. Function: protect from sun damage and trauma. Also, for heat retentionB. Nails:1. Formed from stratum corneum (dead keratinized cells)2. Function: protection and graspingC. Exocrine glands: 1. Sebaceous glands = Oil (= sebum) glandsa. associated with hair folliclesb. Functions: soften the skin & is bactericidal2. Sweat (sudoriferous) glandsa. Merocrinei. found everywhereii. Releases perspiration (sweat) for thermoregulationb. Apocrinei. Axillary and pubic regionsii. Secretes onto hair rootsiii. Releases odorous secretions called pheromones Other Skin Glands:1. Ceruminous glands (cerumen = earwax)a. modified sweat glandsb. in external auditory canalc. cerumen can trap foreign particles and small insects, and it helps to keep the eardrum “soft’2. Mammary glands a. modified sweat glandsb. produce milkWhich of the following cells is found only in the stratum basale and is a light touchreceptor?a. Keratinocyteb. Fibrocytec. Epidermal Dendritic Celld. Tactile Celle.