[An ultrastructural study of penetration and replacement process by trophoblast cell into human maternal vessel (author's transl)].

To elucidate the mechanism of trophoblastic penetration into maternal vessels and the function of the trophoblast replacing the endothelium, feto-maternal junctional zone (FMJZ) removed from human uteri in early gestational stages of 4 to 11 weeks were morphologically investigated. The trophoblast cells which can approach to or penetrate the maternal vessels and can replace the endothelial cell were only syncytiotrophoblast cells. Since microfilaments aggregated in bundle in cytoplasm of the syncytiotrophoblast cells which are approaching to the maternal vessel inserted into dense bodies or dense patches, it is considered that the microfilaments are composed of thin filaments mainly like in smooth muscle cell. Degranulation of rER and lysosomal structure or aggregation of microfilaments are occurred in endothelial cells penetrated or closely contacted by field horsetail-like cytoplasmic processes of syncytiotrophoblast cell, respectively. It is possible that the syncytiotrophoblast cell and maternal endothelial cell have similar origin, since both cell can be in close contact with tight junction and simple apposition like intrinsic endothelial junction.