[Fetal membranes of the human. Electron microscopy study].

The structure of the human fetal membranes was examined after normal and pathological pregnancy. The cellular junctions are desmosomes and gap junctions in the amniotic epithelium, whereas in the chorionic epithelium tight junctions in the form of maculae occludentes are found occasionally in addition to desmosomes and gap junctions. The absence of zonulae occludentes, which could act as an effective permeability barrier, in the fetal membranes indicates that the intercellular spaces of the fetal membranes represent an extracellular route for paraplacental substance exchange. In pathological pregnancy such as diabetes mellitus, rhesus incompatibility and toxemia, the morphological variations of amniotic epithelium compared with normal amnion are manifold and greatly specific. On the contrary, the morphological changes of chorionic epithelium in pathological pregnancy seem nonspecific. They differ in various pathological pregnancies only in quantity. In addition to fibroblasts and Hofbauer cells, the connective tissue of the fetal membranes contain myofibroblasts. Since myofibroblasts possess the ability to contract, we assume that they may contribute to protection of the fetal membranes from overdistension.