Ultrastructure of cellular components of human trophoblasts during early pregnancy.

Two cell types, the cyto- and syncytio-trophoblasts, were identified in human chorionic villi of 6-10 weeks' gestation. The intracellular organization of these cells was examined. Ultrathin sections of small pieces of chorionic villi revealed the presence of a multinucleate syncytiotrophoblastic layer, whose surface was covered with microvilli. The cytotrophoblasts, however, had a single large nucleus with a prominent nucleolus. An interesting feature of the basement membrane of these cells was the presence of aggregates of dark granules in samples of the earlier gestational age (6-8 weeks) and granular bodies having a dense outer ring and a translucent inner ring with a lucid central area in samples of 8-10 weeks' gestation. Both types of granules are mineralized and are assumed to perform a buffering role for maintaining the neutrality of the layer.