The Characteristic Distribution of Alkaline Phosphatase in the Full-Term Human Placenta

The ultrastructural localization of alkaline phosphatase activity was studied in the full-term human placenta. Alkaline phosphatase activity is not only found along the plasma membrane lining the microvilli and in vesicles of the syncytiotrophoblast as in other transporting cells, but also along the basal surface of the syncytiotrophoblast. The latter localization is found adjacent to the basal lamina, except, however, in places where a cytotrophoblast is present, where it follows the outer surface of the cytotrophoblast and only part of the basal lamina.