[Human placenta structure in II and III trimesters of physiological pregnancy].

The placenta of 20 women with normal pregnancy was studied during II and III trimesters to obtain the complex characteristic of the structures participating in the formation of syncytio-capillary membranes. Immunocytochemical endothelial cell marker CD34 and morphometry were used for the assessment of some villous parameters: villous area, villous stromal area, villous epithelial area and vascular endothelium area. The main attention was given to the remodeling of the villous epithelium and capillary network. The significant reduction of the epithelial area and that of the villous stroma was detected simultaneously with intensive their vascularization. Morpho-functionally, most of the terminal villi were specialized, containing sinusoid-type capillaries which were in close contact with attenuated, anuclea regions of syncytiotrophoblast. The proportion of terminal villous endothelium in respect to the stroma was significantly increased. Thus, in II and III trimesters of physiological pregnancy the structural changes take place in the placenta, in particular, the capillaries are transformed into thin-walled sinusoids, that approach and closely interact with syncytiotrophoblast resulting in the formation of the syncytio-capillary membranes necessary for an adequate diffusion and meeting the growing needs of the fetus.

[Morphogenesis of human placenta in the first trimester of gestation].

On the basis of morphometric and immunohistochemical study of placental villi obtained from 45 cases of medicinal and medical abortions in healthy women, the new data on placentation are presented with the discrimination of three stages of placental morphogenesis. The first stage (weeks 4 and 5 after fertilization) included a differentiation of villous chorion (chorion frondosum). It was characterized by high mitotic activity of villous cytotrophoblast and intensive vasculogenesis in the villous stroma. The second stage (weeks 6 and 7) included capillary development (angiogenesis) and formation of vascular communications within a "placenta-embryo" subsystem functioning in low-oxygen level environment. The third stage (weeks 8 and 9-10) was characterized by vascular bed formation in "mother-placenta" subsystem and by the beginning of more effective hemochorial embryo and fetal metabolism. As a result of placentation, hemodynamics formation in "mother-placenta-embryo" system was completed, which is a necessary condition for further fetal development.