From Big Medical Encyclopedia

PIGMENT CELLS (cellulae pigmentosae; lat. pigmentum paint) — the cells of animals and the person synthesizing pigments and containing these pigments in cytoplasm. The pigments synthesized by P. to., cause generally coloring of skin and its derivatives, color of eyes.

There are three types P. to.: melanophores, xanthophores and iridofor. Melanophores synthesize melanina (see) — pigments of dark brown or black color; xanthophores synthesize pigments of yellow, orange and red color, iridofor — pigments of silvery color. From true P. to. nek-ry scientists suggest to distinguish chromatophores (see) — the cells which are containing, but not synthesizing pigments, napr, the gemosiderofor containing hemosiderin, and the lipokhro-mofor containing lipokhromny pigments.

All three types P. occur at the lowest vertebrata to., including the melanophores having the expressed ability to redistribution of a pigment in a cell. Movement of a pigment from the center of a cell is followed by its dispersion, and reverse — concentration that is the cornerstone fiziol, the mechanism of discoloration of some animals (e.g., a chameleon). Dispersion of a pigment happens under the influence of the melanotsitostimuliruyushchy (melanotropny) hormones synthesized by an intermediate share of a hypophysis, concentration — under the influence of hormone of an epiphysis — melatonin.

The only P. to. mammals and the person — melanocytes, their analogs at the lowest vertebrata are melanophores i.e. melanocytes which finished a differentiation. Thanks to ability of melanin to absorb the UF-part of a range of a sunlight, P. to. the person perform protective function, protecting skin and an organ of sight from the damaging influence of sunshine. These cells contain specific cytoplasmatic organellas — the melanosoma producing melanin. Electronic microscopically melanosoma represent high-contrast granular educations of 15 in size — 25 nanometers, a thicket near a kernel. Melanin is synthesized on a proteinaceous matrix melanosy of tyrosine under the influence of a tyrosinase and laid in the form of a melanoproteinovy complex. The inert melanosoma which are completely filled with melanin and euzymatic seen in a light microscope are called melaninovy (pigmental) granules. Participate in regulation of synthesis of melanin melanotsitostimuliruyushchy hormones (see), sex, steroid and other hormones.

Depending on an origin distinguish free and epithelial melanocytes. Free melanocytes are formed of the melanoblasts migrating from a nervous crest in various parts of a body of a germ and which are transformed at later stages of development to mature P. to. - melanocytes. At the lowest vertebrata also melanophores, xanthophores, iridofor are formed of cells of a nervous crest.

Free melanocytes can have various form — from round to star-shaped with the short or branching shoots, are capable to movement. They are a part of epidermis, a derma, hair follicles, meninx, stromas of an iris, an idiovascular cover of an eye, causing their color. At the lowest vertebrata they are also a part internal a vystilok of a body. At the person epidermal melanocytes form base and functional epidermal melaninovy unit in a complex with cells of basal and acanthceous layers of epidermis, to-rye way of phagocytosis take the melanosoma synthesized by melanocytes and by that regulate the speed of synthesis of melanin — the main pigment of skin of the person. The average relation of number of epidermal melanocytes to number of cells of basal and acanthceous layers of epidermis equally 1:36 irrespective of race. Various skin color of people of different races is defined by degree of productivity of melanocytes.

Strengthening of coloring of skin at action solar, UV rays, hormonal disturbances in an organism (see. Melanosis ) it is connected not with increase in quantity of melanocytes, and with increase in number melanosy and their redistribution in melanocytes and cells of basal and acanthceous layers of epidermis.

Disturbance of migration of melanoblasts in the course of an embryogenesis leads to formation of a nevus of skin and mucous membranes (see. Nevus ). The malignancy of melanocytes is possible that it leads to development of a malignant tumor — melanomas (see).

Epithelial melanocytes develop from an eye rudiment, forming a pigmental epithelium of a retina, an iris, a ciliary body of animals and the person. Melanocytes of a retina have the polygonal form, on their inner surface there are thin cytoplasmatic shoots. Melaninovy granules fill all cell, getting into its shoots; they are the light-absorbing screen, and also ions of heavy metals and nek-ry poisons are capable to detain.

See also Pigmentation , Pigments .

Bibliography: Brown F. A. Chromatophores and decolourization, in book: Comparative fiziol, animals, under the editorship of JI. Prosser, the lane with English, t. 3, page 518, M., 1978, bibliogr.; Miller B. E. Intermedii, Chisinau, 1973; Mikhaylov I. N. Structure and function of epidermis, M., 1979; Stroyeva O. G.

Morphogenesis and congenital anomalies of an eye of mammals, M., 1971.

A. A. Klishov