Sequential Ultrastructural Change of Chorionic Villi in Human Placenta by Gestational Period

Park, Tae Dong; Kwon, Tae Jung; Chi, Je G

Abstract

A study was performed to observe the sequential morphological change of the human placental barrier by means of light microscopy, immunohistochemistry, scanning electron microscopy and transmission electron microscopy. The examined placentas ranged in age from 4 weeks gestation to the full-term(40 weeks). Sixty seven placental specimens were obtained immediately after delivery. With the progression of gestation, the microvilli on the surface of syncytinum tended to be fewer, shorter and blunter. The syncytiotrophoblasts were getting thinner with formation of vasculo-syncytial membrane. The cytotrophoblasts formed a continuous layer which progressively disappeared but still present in the mature villi. In view of presence of intermediate cells and remnant of desmosomes, the cytotrophoblasts appeared to form the syncytiotrophoblasts. In early pregnancy, capillary formation took place by the aggregation and differentiation of the proliferation and aggregation of endothelial cells and pericytes. Myofibroblasts in villous stroma were examined by desmin immunohistochemical staining, and detected from 19 weeks to the full-term. During last period of pregancy definitive smooth muscle cells could be demonstrated, suggesting that the presence of myofibroblasts or smooth muscle cells are closely related to the placental maturity. Scanning electron microscopy of the early placenta showed numerous syncytial sprouts representing stages in the formation of new villi, but in the late period of gestation syncytial sprouts were diminished. It is concluded that the syncytiotrophoblast is originated from the cytotrophoblast in early pregnancy as the placental barrier is formulated. Moreover, myofibroblasts and smooth muscle cells in villous stroma play important role in placental maturation.