Comparative study of human trophoblasts according to their microenvironment: Light and electron microscopic study

Trophoblasts, being the basic component of the placenta and fetal membranes, carry out different functions depending on their location and it is well known that they acquire unique structural features during development reflecting these functions. The goal of the present study was determined as obtaining new structural hints about the functions of a variety of structures of trophoblastic origin (syncytiotrophoblast, syncytial knot, syncytial buds, syncytial bridges etc.); extravillous trophoblasts (chorionic plate, fibrin, decidua, invaded blood vessel etc.) and the other stromal components including endothelium by a comparative examination at light and electron microscopic levels. In the present study, placenta samples were obtained from ten healthy full-term cesarean births were used which did not have any chronic disease or complications during pregnancy or at delivery. Frozen sections obtained from tissue samples were stained with hematoxylin-eosin, semi-thin sections of the same samples were stained with toluidine blue for light microscopic examinations. Uranyl acetate-lead citrate stained thin sections were examined and photographed using an electron microscope. In this study, types of villi forming the villus tree, stromal cells, chorionic plate and decidua were observed structurally normal. We determined the signs of the transformation of cytotrophoblast to syncytiotrophoblast is still lasting in the term placenta; the development of matrix type fibrinoid from fibrin type fibrinoid and migration of trophoblasts in response to this hypoxic cell damage. The marks of the endothelium-syncytiotrophoblasts transformation was found in decidual vessels and syncytial lining of the intervillous space adjacent to the decidua. Signs of new blood vessel formation in the floating villi by vasculogenesis rather than angiogenesis was determined in the term placenta. Stromal cells like reticulum cells, fibroblasts, myofibroblasts, pericytes and trophoblasts were observed to be sharing similar ultra-structural features. Thus; besides their common origin, the similarities at fine structural level lead us to think that trophoblasts, stromal cells and endothelial cells involved in neovascularisation are cells that can easily differantiate to each other under appropriate conditions in their special microenvironment.