METAPLASIA (metaplasia; grech, metaplasso to transform, turn) — permanent transformation of one type of fabric into another, differing from initial morphologically and functionally. The m is adaptive process, with the help to-rogo fabric survives in the changed living conditions thanks to restructuring, unlike gistol, accommodations, at a cut of a cell do not change tkanespetsifichesky structural properties. The term was for the first time offered in 1884 by Virkhov. The doctrine about M. was intensively developed in the first half of 20 century in D. P. Hansemann's works, Ribberta (M. by W. H. Ribbert), E. Krompecher, H. G. Hlopin, G.E. Koritsky, etc.
Distinguish direct and indirect M. Direct M. is characterized by change of character of fabric without reproduction of its cells. A typical example of direct M. is transformation of connecting fabric in bone without participation of osteogene elements. At indirect, or neoplastic, M. is observed proliferation of cells with their reproduction and a differentiation. Neogenic fabric can sometimes reach higher extent of development, than it was peculiar to initial fabric, napr, formation of hepatic fabric at M. of an epithelium of bilious channels, formation of pancreatic islands at M. of an epithelium of pancreat ducts. Then process is designated as prozoplastichesky by M. In some cases the differentiation of cells turns out lower, than in initial fabric that name regressive M., napr, at development of a multilayer flat epithelium on site of a cylindrical ciliary epithelium of a mucous membrane of respiratory tracts.
The reason leading to M. are most often hron, an inflammation, dishormonal changes, tumoral process, avitaminosis And.
Depending on localization of changes allocate M. of an epithelium, to connecting fabric with its transformation into bone and cartilaginous tissue and so-called myeloid M. with transformation of lymphoid cells into cells of a miyelopoetichesky row. Epithelial M. meets more often, the cut can be an example transformation of an epithelium grease and sialadens in conditions hron, inflammations in a multilayer flat keratosic epithelium, an epithelium milk and sweat glands at dishormonal changes — in a pale epithelium of apocrine type. So-called intestinal M., or an enterolization of a mucous membrane of a stomach, napr is known, at gastritis, and also the epidermoid M. of an epithelium of a gall bladder, bilious ways and pancreat ducts arising at hron, an inflammation. The transitional epithelium of uric ways at hron, an inflammation can be exposed to M. both in a flat multilayer epithelium, and in ferruterous prismatic. In mesodermal an epithelium the possibility of transformation of a mesothelium into fibroblasts is noted.
According to a number of authors, M. can be carried out over a wide range and possibly transformation of an epithelium into connecting fabric (see. Mesenchymoplasty ). Other authors limit M. to a framework of gistogenetichesky type, denying a possibility of transformation of an epithelium, napr, entodermalny type, in epidermal. Nek-ry authors deny M.'s possibility, explaining emergence of an epithelium alien to this place with an embryonal allotopia, a heteroplasia, a prosoplasia, a plyuripotentnost of cambial elements and various directions of their differentiation. The greatest recognition was gained by the point of view acknowledging the possibility of broad transformations of epithelial fabric, but denying probability of transformation of an epithelium into connecting fabric.
The wedge, value M. depends on an etiology and localization patol, process. In a mucous membrane of the channel of a neck of uterus and in an endometria find sites of a multilayer flat epithelium at a prolapse of the uterus, a pyometra, tuberculosis, etc. More often at the same time the true M. which is carried out by means of reserve cells is observed. According to nek-ry authors, the epithelium of a neck of uterus at dishormonal disturbances can be exposed to M. in ferruterous prismatic; an epithelium of glands of an endometria — in an epithelium of glands of a neck of uterus and uterine tubes; an epithelium of glands of a neck of uterus — in an epithelium of glands of an endometria and uterine tubes. The epithelium of an epididymis at hron, an inflammation can gain looking alike a transitional epithelium of urinary tract. The m of an epithelium of a mucous membrane of an oral cavity and a neck of uterus in a multilayer flat keratosic epithelium is pretumor disease (see); an adverse predictive sign is emergence of the centers of planocellular M. in layers of transitional cell cancer.
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D. I. Golovin.