[Function of the cytotrophoblast in the amniotic fluid/fetus compartment]

In the trophoblast cells of the fetal membranes, PAS-positive substances are demonstrated which are released intermittently into the intercellular space. It is incorrect to designate them as fibrinoid, since degeneratively altered material is not involved. This intracellular substance is with certainty the morphological substrate of the barrier in the region of the feto-maternal contact. It exerts a filter action and probably also acts in the sense of an immune barrier: lymphocytes cannot migrate through it in large numbers. The intercellular substance is flushed out with a flow of fluid through the remaining layers of the fetal membranes into the amniotic fluid. It passes into the fetus by swallowing movements and forms a major proportion of the meconium.