The stratum basale (bah-SAY-lee) consists of a single layer of cuboidal to low columnar cells resting on the basement membrane of the epithelium. There are three types of cells in this layer:
- Keratinocytes (keh-RAT-ih-no-sites) are the majority of cells. They are named for their role in synthesizing the keratin of the skin. Keratinocytes of the stratum basale undergo mitosis and produce new epidermal cells to replace the dead ones that exfoliate (flake off) from the surface.
- Melanocytes (MEL-an-o-sites) synthesize the pigment melanin. They have long branching processes that spread among the basal keratinocytes and continually shed melanin-containing fragments from their tips. The keratinocytes phagocytize these fragments and accumulate melanin granules on the "sunny side" of the nucleus. Like a little parasol, the pigment shields the DNA from ultraviolet radiation. People of all skin colors have about equal numbers of melanocytes. Differences in color result from differences in the rate of melanin synthesis and how clumped or spread out the melanin is in the keratinocytes. In light skin, the melanin is less abundant and is relatively clumped near the nucleus, imparting less color to the cells.
- Tactile (Merkel2) cells, relatively few in number, are receptors for the sense of touch. The tactile cell and its dermal nerve fiber are collectively called a tactile (Merkel) disc.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.
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