[Reabsorption of amniotic fluid through parietal fetal membranes. A hypothesis based on an ultrastructure study]

Recent investigations have shown that the link between water transport and solute transport in epithelia is made possible by subcellular structure build on a striking geometrical plan, namely, long and narrow dead end channels. The most striking feature of our electron microscopic study of the amnion as well as the chorionic cytotrophoblast, was the demonstration of the existence of intercellular channels running between the lateral sides of the cells with typical junctional complexes sealing their proximal ends; thus they constitute long and narrow dead-end channels. In the amnion, these channels open through the basal lamina into the connective tissue, and in the chorionic cytotrophoblast they open in the direction of the decidua. This situation seems to indicate that fluid emerges from the open mouth of the amniotic intercellular channels and then continues to flow into the channels of the cytotrophoblast, across its podocytic processes, to be dumped into the decidua, and finally drained by maternal decidual vessels. This morphological study suggests that parietal fetal membranes might be an important route for transport of solute and fluid from the liquor amnii into the maternal circulation.