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Melanocytes |
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Melanocytes
in vertebrates and man, pigment cells that synthesize melanins. There are two kinds of melanocytes: free melanocytes and epithelial melanocytes. Free melanocytes, which are found in the skin, hair follicles, meninges, choroid, and stroma of the iris, originate from the neural crests. When the neural tube closes, they migrate to different parts of the body in the form of mobile, colorless cells, or melanoblasts—the precursors of melanocytes. Epithelial melanocytes, which are found in the pigmented epithelium of the retina, iris, and ciliary folds of the eye, originate from cells of the rudimentary eye. Melanins are synthesized in the melanocytes in special organelles, or melanosomes, which contain the enzyme tyrosinase. After they fill with melanin, the melanosomes become enzymatically inert pigment granules. The number, shape, and intensity of color of these granules, like the general color of the body, are genetically controlled. Melanocytes are colorless in albinos, in which melanins are not synthesized because of an absence of active tyrosinase. O. G. STROEVA Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content. |
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