8.2.1 Strata
- Stratum Basale (stratum germinativum)
- deepest single layer of epidermis – contains merkel cells, melanocytes, keratinocytes & stem cells that divide repeatedly
- Stratum Spinosum
- provides strength and flexibility to the skin
- 8 to 10 cell layers are held together by desmosomes (site of adhesion of adjacent cells)
- melanin is deposited from nearby melanocytes.
- Stratum Granulosum
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- transition between the deeper, metabolically active strata and the dead cells of the more superficial strata
- 3-5 layers of flat dying cells that show nuclear degeneration
- this layer is an example of apoptosis (cell destruction)
- contains lamellar granules that release lipid that repels water.
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- Stratum Lucidum
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- present only in the fingers tips, palms of the hands, and soles of the feet.
- three to five layers of clear, flat, dead cells.
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- Stratum Corneum
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- 25 to 30 layers of flat dead cells filled with keratin and surrounded by lipids
- continuously shed
- barrier to light, heat, water, chemicals & bacteria
- constant exposure to friction will cause this layer to increase in depth with the formation of a callus, an abnormal thickening of the epidermis.