FETAL MEMBRANES

From Big Medical Encyclopedia

FETAL MEMBRANES — the covers arising at an early stage of an embryogenesis, developing according to requirements of a germ (fruit) and providing conditions of its development. Items of the lake are a component afterbirth (see). The amnion and chorion developing from extraembryonic embryonal components and also the mucous membrane of a uterus which is exposed during pregnancy to transformation in belong to fetal membranes decidua (see).

Amnion (grech, amnion a bowl for sacrificial blood; synonym: a water cover, an amniotic cover) — the internal P. of the lake forming the cavity containing amniotic waters (see) in which the fruit develops. The rudiment of amnion is formed of an extraembryonic ectoderm and an extraembryonic mesoderm (see. Germinal leaves ). From an ectoderm the epithelium of amnion, from a mesoderm — its connective tissue basis develops.

Macroscopically amnion represents thin, almost transparent cover which adjoins to chorion, covers an inner surface of a placenta, passes to an umbilical cord, covering it in the form of a case and merges in a navel with investments of a germ. Microscopically amnion consists of 5 layers: its inner surface is covered with an epithelium under which the basal membrane, a compact layer, fibroblasts, a spongy layer are located. An epithelium of amnion at early stages of development flat, in the subsequent it becomes single-row cubic and cylindrical. At the same time the vneplatsen-tare zone of amnion is covered by a cubic epithelium, and placental — a cylindrical epithelium where along with cylindrical cells puzyrkoobrazny meet. Connect with function of puzyrkoobrazny cells generally formation of amniotic waters. Cells of an epithelium of amnion during secretion become higher, in their cytoplasm vacuoles are formed, to-rye merge, push aside a kernel to the periphery, cause a rupture of a cell membrane; contents of vacuoles together with a part of cytoplasm pass into a cavity of amnion. The destroyed cells are exfoliated and replaced with new. Cytoplasm of cells of an epithelium of amnion contains lipids, polysaccharides, glikozaminoglikana, and also numerous enzymes like lipase, peptidases, trypsin, and also glycolytic enzymes. The basal membrane is located under an epithelium in the form of narrow eosinophilic acellular weight. The compact layer is presented by the homogeneous weight deprived of cells, differing from a basal membrane in more pale coloring. The layer of fibroblasts the thickest also consists of the fibroblasts which are located in dense network of collagenic, reticular fibers and intercellular substance; sometimes in it histiocytes meet. The spongy layer of amnion is connected by means of connective tissue fibers and intercellular substance with smooth chorion. Amnion contains the antigens (And yes In) corresponding to the group antigens which are contained in blood of a fruit.

Chorion (grech, chorion an afterbirth) — the cover of a fetal origin arising at an early stage of an embryogenesis (a stage of a morula and a blastocyste) on the basis of a trophoblast and a mesoblast. After implantation of an oospore on a surface trophoblast (see) primary vorsina appear, by 12th day of pre-natal development in them elements of a mesenchyma — the beginning of emergence of chorion appear. By the end of the 2nd week of pregnancy the secondary vorsina of chorion shipped in intervillous space are formed. Vorsina of chorion have a two-layer epithelial cover: sincytium and cytotrophoblast (layer of cells of Langkhans); their stroma consists of a mesenchyma in which there are fibroblasts and blood vessels. Within the first weeks of pregnancy of a vorsina of chorion are distributed on a surface of fetal egg evenly. Since the end of the II month of pregnancy of a vorsina in the field of a capsular decidua gradually atrophy and disappear, chorion in this area becomes smooth. Vorsina in the field of a basal decidua expand, creating placenta (see). Smooth chorion an inner surface adjoins to amnion, on - necessary — to a decidua. In it distinguish four layers: cellular, reticular, pseudo-basal membrane, trophoblast.

The cellular layer of smooth chorion is well differentiated in early durations of gestation, in late terms in P. of the lake it quite often is absent. The reticular layer is the strongest, it contains fibroblasts and Kashchenko's cells — Hofbauera. A pseudo-basal membrane — a thin homogeneous coat, free of cells. The trophoblast vaguely separates from an adjacent decidua. According to Yu. V. Guljkevich, cells of a trophoblast are located in several layers (5 — 10), differ in polymorphism, cytoplasm supports them a significant amount of ribonucleoproteins, high-molecular polysaccharides, a glycogen, and also an alkaline phosphatase, nonspecific esterases and other enzymes. The structure and functional activity of a trophoblast remain until the end of pregnancy. Believe that the trophoblast of smooth chorion synthesizes chorionic gonadotrophin (see).

And a decidua, adjacent to it, acid glikozaminoglikana, napr, hyaluronic to - that and hondroitinsulfata, and also various glycoproteins and a glycogen are found in connecting fabric of smooth chorion. Group antigens of a fruit in smooth chorion usually are absent therefore fabric it does not exert the immunizing impact on an organism of the pregnant woman.

Functional value

the Most important function of an epithelium of amnion is secretion of the amniotic waters defining the most important conditions of fetation, and also removal of the products of its exchange getting to amniotic waters. The resorption of waters occurs through an epithelium of amnion, further liquid gets into the spongy layer adjoining on smooth chorion and is removed through fabric of smooth chorion. Secretion and a resorption of amniotic waters define formation of waters in the quantity necessary for ensuring life activity of a fruit at all stages of its development. Removal together with amniotic waters of products of metabolism indicates P.'s participation by the lake in providing a homeostasis of the developing fruit.

Chorion carries out trophic, secretory, respiratory and protective functions.

Data on activity of fermental systems in amnion and smooth chorion indicate also existence of processes of the paraplacental exchange which is carried out through P. by the lake

of P. of the lake together with amniotic waters play an essential role during childbirth (see). At labor pains amniotic waters direct towards an internal opening of a neck of uterus where the lower part of P. of the lake is located. This part of covers which is implemented together with amniotic waters into the canal of a neck of uterus carries the name of a bag of waters.

The bag of waters has usually spherical shape and is broken off in labor at the end of the period of disclosure of a neck of uterus.

Pathology

disturbance of processes of secretion and a resorption of amniotic waters, preferential amnion is connected With change of functions P. of the lake. It can lead to insufficient products of waters — to an oligoamnios (see) or to their surplus — hydroamnion (see. Hydramnion ). These disturbances as well as amniotic unions, banners between amnion and various parts of a fruit (see. Amniotic threads, banners, unions ), quite often accompany malformations of a fruit (see. Malformations ). Refer the inflammatory process arising in amnion and chorion to frequent types of pathology of P. of the lake (horioamnionit) which is characterized by symptoms of intoxication and putreform allocations from patrimonial ways.

At the excessive density of P. of the lake the bag of waters gets a cylindrical or pear-shaped form (under the pressure of amniotic waters), the rupture of covers can be overdue that can sometimes promote premature placental detachment. The flat bag of waters arising owing to trace amount of front amniotic waters slows down process of disclosure of a neck of uterus in the first period of childbirth, and also a timely rupture of covers of a bag of waters.

The rupture of fetal membranes belongs to frequent types of obstetric pathology premature (prior to patrimonial activity) and early (before full disclosure of a neck of uterus) (see. Premature bursting of waters ). The rupture of covers of a bag of waters (timely, untimely) depends on

P.'s structure of the lake, extent of increase in intrauterine pressure, and also speed and the nature of formation of the bag of waters.

See also Embryonic development .



Bibliography: E. Platsent's patter of the person, the lane with polsk., Warsaw, 1970; Gulke in and the p Yu. Century, Maccabee-in and M. Yu. and Nikiforov of B. I. Patologiya of an afterbirth of the person and its influence on a fruit, Minsk, 1968; Zhemkova 3. The item and T about p h and e in and O. I. Kliniko-morfologichesky diagnosis of insufficiency of a placenta, page 9, etc., JI., 1973; Dallenbach-Hellweg C. a. N e t t e G. Morphological and histochemical observations on trophoblast and decidua of the basal plate of the human placenta at term, Amer. J. Anat., v. 115, p. 309, 1964; Fox H. Pathology of the placenta, L. a. o., 1978; Handbuch der speziellen pathologischen Anatomie und Histologie, hrsg. v. F. Henke u. O. Lu-barsch, Bd 7, T. 5, B. u. a., 1967.


V. I. Bodyazhina.

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