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study guide 2 - BISC 106 Fall 2005 Kelley Exam II Cheat...

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BISC 106 Fall 2005 Kelley Exam II Cheat sheet 1.) Functions of Skin Temperature Regulation-with blood and sweat Protection Makes vitamin D Sensation 2.) Thickness of Dermis vs. Epidermis Dermis=much thicker than Epidermis 3.) 4 cell types of epidermis, function of each cell Keratinocytes= about 90% of epidermal cells, arranged in 4-5 layers, produce Keratin (a tough fibrous protein that helps protect the skin and underlying tissues from heat, microbes, and chemicals.) Also produce Lamellar granules, which release water proof sealant. Melanocytes= 8% of epidermal cells. Produce Melanin (brown-black pigment that contributes to skin color and absorbs damaging UV light). Melanocytes are particularly susceptible to damage by UV light. Langerhans Cells= participate in immune responses mounted against microbes that invade the skin. Easily damaged by UV light. Merkel Cells= contact the flattened process of a sensory neuron, a structure called a tactile (Merkel) disc (a modified epidermal cell in stratum basale of hairless skin that functions as a cutaneous receptor for discriminative touch). 4.) 5 strata of epidermis Stratum basale= deepest layer, single row of cuboidal or columnar keratinocytes. Some cells in this layer are stem cells that undergo cell division to continually produce new keratinocytes. Stratum Spinosum- superficial to stratum basale. 8-10 layers of many sided keratinocytes fit closely together. (more superficial layers are more flattened). Stratum Granulosum- middle. 3-5 layers of flattened keratinocytes that are undergoing apoptosis (genetically programmed cell death in which nucleus fragments before cells die). Nuclei and other organelles begin to degenerate. Presence of keratin in cells. Also membrane enclosed Lamellar Granulles (release lipid rich secretion that acts as water-repellent sealant, regarding loss of body fluids and entry of foreign materials. Stratum Lucidum- only in thick skin of fingertips, palms, and soles. 3-5 layers of flattened clear, dead keratinocytes that contain large amounts of keratin.
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Stratum Corneum= 25-30 layers of flattened dead keratinocytes. Continuously shed and replaced by cells from deeper strata. Interior of cells are mostly keratin. Protects deeper layers from injury and microbial invasion. 5.) Maturation of keratinocyte 6.) Lifespan of a keratinocyte, contents of keratinocyte at various stages (strata)- newly formed cells in the stratum basale are slowly pushed to surface. As the cells move from one layer to the next, the accumulate more and more keratin in a process called keratininzation. Eventually keratinized cells slough off and are replaced by underlying cells that, in turn become keratinized. Process takes about 4 weeks in an average epidermis of 0.1mm (0.004in) in thickness.
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