ULTRASTRUCTURE OF CELLULAR-COMPONENTS OF HUMAN TROPHOBLASTS DURING EARLY-PREGNANCY

Two cell types, the cyto- and syncytio-trophoblasts, were identified i n human chorionic villi of 6-10 weeks' gestation. The intracellular or ganization of these cells was examined. Ultrathin sections of small pi eces of chorionic villi revealed the presence of a multinucleate syncy tiotrophoblastic layer, whose surface was covered with microvilli. The cytotrophoblasts, however, had a single large nucleus with a prominen t nucleolus. An interesting feature of the basement membrane of these cells was the presence of aggregates of dark granules in samples of th e earlier gestational age (6-8 weeks) and granular bodies having a den se outer ring and a translucent inner ring with a lucid central area i n samples of 8-10 weeks' gestation. Both types of granules are mineral ized and are assumed to perform a buffering role for maintaining the n eutrality of the layer.