a. Modified sweat glandsb. In external auditory canalc. Cerumen is an insect repellant and helps keep the eardrum “soft”a. Keratinocyteb. Fibrocytec. Epidermal dendritic (Langerhans) celld. Tactile (Merkel) celle. MelanocyteINTEGUMENTARY SYSTEMI IntroductionA. Integument = covering = skin (largest organ of 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 layers B. Dermis1. Middle layer2. Composed primarily of dense irregular connective tissue3. Contains nerve endings, hair follicles, & 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 tissues3. Composed of areolar CT and adipose CTIII Layers of EpidermisA. Stratum Basale: single layer of columnar/cuboidal cells resting on thebasement membrane; cells are very mitoticB. Stratum Spinosum: several layers of polygonal-shaped cells with spines. Small degree of mitosis here.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 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 (90%); found in all layers; produce keratin2. Melanocytes: 2nd most numerous (8%); found only in the stratum basale; produce melanin (protect against UV light)3. Tactile (Merkel) Cells: 3rd most numerous (1%); found only in the stratumbasale; provide information regarding tactile (light touch) sensation4. Epidermal dendritic (Langerhans) cells: 4th most numerous (<1%); found primarily in the stratum spinosum; phagocyteV 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 rootsB. Reticular Layer: deepest; contains blood vessels; sensory receptors (neurons); secretary 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 UV light, trauma, and heat lossB. Nails:1. Formed from the stratum corneum2. Function: protection and graspingC. Exocrine glands: 3 kinds1. Sebaceous glands = Oil (= sebum) glandsa. Associated with hair folliclesb. Functions: soften the skin & bactericidal2. Sweat (sudoriferous) glandsa. Eccrinei. found everywhereii. release perspiration (sweat)b. Apocrinei. Axillary & pubic regionsii. Secretes onto hair shaftsiii. Releases an odiferous secretion3. Ceruminous (cerumen = earwax)a. Modified sweat glandsb. In external auditory canalc. Cerumen is an insect repellant and helps keep the eardrum “soft”Which of the following cells is found only in the stratum basale and is a light touchreceptor?a. Keratinocyteb. Fibrocytec. Epidermal dendritic (Langerhans) celld. Tactile (Merkel) celle.