TROPHOBLAST (Greek trophe food, food + blast os sprout, germ; synonym: a trophectoderma, a chorial
epithelium) — the outside cellular mass of a germ. T. forms a continuous cellular cover of all germinal complex, further creates an epithelial cover of fibers of chorion, and afterwards — fibers of a placenta.
T. placental mammals it is homologous to an ectodermal epithelium of a serous (chorial) cover of reptiles, birds, marsupials, but differs in extremely early isolation from other material of a germ and an early differentiation.
During crushing of a germ (see) the person by the end of the 1st week of pre-natal development its cellular material is differentiated on emb-rioblast (internal cellular weight) and a trophoblast (outside cellular weight). T. it is presented by numerous small light blastomeres with the hydrated cytoplasm, to-rye acquire accumulation of smaller large basphilic cells of embriobla-hundred. In a blastocyste of a cell of T. become flattened (see Crushing of egg).
At implantation of a blastocyste at the person, edge begins on 6 — the 7th days from the moment of fertilization, T., contacting to a mucous membrane of a uterus, expands, forming the tyazh of cells branching and connecting with each other, and it begins to be differentiated on a cytotrophoblast and a syntrophoblast. Cells of a cytotrophoblast contact like epithelial cells, actively share. Its superficial cells merge and create the syntrophoblast consisting of multinucleate or colossal cells of various size and a form. The syntrophoblast in the place of contact with tissues of a mucous membrane of a uterus actively expands and, forming outgrowths, is implemented into depth of an endometria (see Pregnancy). The hydrolases produced by it provide at the person destruction not only an epithelium and connecting fabric of an endometria, but also walls of blood vessels. T. without having shipped - shikhsya a blastocyste remains thin and keeps cellular structure.
In process of immersion of a blastocyste in a mucous membrane of a uterus all new sites of a cytotrophoblast give rise to a syntrophoblast, thus, the majority of cells of a cytotrophoblast is spent for formation of a powerful syntrophoblast (a plaz-modiotrofoblast, an implantation plazmodialny layer). In it gradually there is a system of the lacunas connected with each other which are filled with maternal blood from the destroyed vessels of a mucous membrane of a uterus.
Since 9th day of pre-natal development growth of the cytotrophoblast forming massive reniform growing into thickness of a syntrophoblast becomes more active. This process becomes so intensive that the ratio of mass of a syntrophoblast and a cytotrophoblast changes in favor of the last.
At formation of a placenta (see) in outgrowths of T. (primary fibers) the extraembryonic mesenchyma grows (see), creating their connective tissue basis therefore secondary fibers are formed, to-rye call fibers of chorion, and the differentiated cellular layers of T. — chorial epithelium.
Structure of T. in different sites of a placenta of the person is defined by his relationship with the next fabrics, depends on its localization and term of development of pregnancy. Morfol. variety of cells of T. probably it is connected with the broad range of its functions.
Functions T. (the chorial epithelium differentiated from it) are diverse: it provides implantation of a germ, producing proteolytic enzymes, the lyseing fabrics of an endometria; provides bilateral gas exchange with blood of mother, and also food of a germ and release it from products of exchange; takes part in production of the hormones providing maintenance of a necessary condition of an ovary and an endometria during pregnancy allows to keep an immunohomeostasis in system mother — a fruit, etc.
Pathology of T. — see. Trophoblastic disease.
Bibliography: Brusilovsky A. I.
• Functional morphology platsentar
leg of a barrier of the person, Kiev, 1976; The island about r to and E. Platsenta of the person, the lane with polsk., Warsaw, 1970; e m to the island and 3. P. A histologic structure of a trophoblast of smooth chorion at the person, Dokl. Academy of Sciences of the USSR, t. 113, No. 5, page 1140, 1957; Knorre A. G. Embryonal histogenesis, L., 1971; C and p e l N and -
to about in N. I. Gistofiziologiya of a placenta of the person, Novosibirsk, 1980.
O. V. Volkova.