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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.


References in periodicals archive ?
Pegs on the inner, anticlinal walls of epidermal cells appear to be found only in the extant genera, Encephalartos, Lepidozamia, and Macrozamia.
To compare leaf samples, the researchers calculated what they call the stomatal index-a value that depends on the number of stomata and the total number of epidermal cells in a particular patch of leaf.
The current understanding of the disease is that increasing levels of androgen sex hormones at puberty lead to increased production of oils and epidermal cells lining the follicles.
We targeted inner ear hair cells, beta cells in the pancreas, and epidermal cells.
Vivendin is proven to activate the longevity genes (Sirtuins) of the epidermal cells using Ineocell Technology, a cell targeted delivery mechanism.
Clapham believes the waviness resulted from abnormal functioning of the epidermal cells at the base of the hair follicle, normally rich in TRPV3, causing the follicles to point in different directions and preventing them from smoothly extruding hair.
The subsequent asymmetric cytokinesis is critical to the divergence in development of the sibling cells, since the longer cell can undergo one or more mitoses, with the progeny all developing as hairless epidermal cells (Avers, 1963).
This, they reasoned, could account for the chemical's ability to normalize the multiplication of overly productive epidermal cells, clearing up the scaly and often painful skin lesions of psoriasis.
Epicel is supplied in grafts, which each consist of a sheet of cultured epidermal cells attached with stainless steel surgical clips to a backing of petrolatum gauze.
The upper portion of the papilla is covered with a thin layer of epidermal cells which divide rapidly.
For epidermal growth, at least 50,000 young epidermal cells per square cm must be injected into the membrane, which feels and looks much like a wet paper towel.