[Organization and cytochemical features of barrier structures in human placenta].
The aim of the present study was to investigate structural pattern of human placental barrier elements using light and electron microscopy and immunocytochemistry. Some important peculiarities of organization of the placental barrier were detected: difference in structure and amount of collagen IV in the basal lamina of endothelium and trophoblast, occurrence of smooth muscle actin in the capillary wall forming syncytiocapillary membranes. In the intercapillary stroma of terminal villi, both fibroblasts and macrophages but not myofibroblasts were found. Since smooth muscle cells and myofibroblasts are absent, pericytes are most likely cells to contain smooth muscle actin in the area of syncytiocapillary membranes.