[Morphology of the materno-fetal metabolic barrier in the human placenta].

On chorionic villi of normal human placentas obtained from different aged females morphological studies were made with a view to collecting new data on the molecular structure and material composition of the materno-fetal metabolism barrier. The basement membrane of the chorionic epithelium is characterized by a network of fine collagen filaments arranged parallel to the plane of the membrane and having diameters less than 200 A. Lying between the filament proteins are lipid molecules in the form of bimolecular lamellae, which with their longitudinal axes are oriented approximately vertical to the plane of the membrane and whose thickness is about 40 A. There are many bimolecular lipid layers. In addition, noncollagenic proteins and uronic-acid-free polysaccharides were also found in the epithelial basement membranes. The submicroscopic organization of the endothelial basement membrane of fetal capillaries is different from that of the epithelial basement membrane of chorionic villi. Whereas lipid components disposed vertically to the plane of the membrane and parallelly oriented protein filaments are also present, collagen seems to be nonexistent as is evident from polarization-optical results. Running parallel to the surface of villi and in the apical sections of the plasmodium are protein filaments which are arranged in the form of a network and probably have certain mechanical functions. The structure of the outer membrane is similar to that of the basement membranes because of the presence there in of oriented lipid inclusions. In the region of microvilli and in the outer zone of the plasmoditrophoblast of young placenta there has been found N-acetyl neuraminic acid. The so-called "placental fibrinoid" in the intervillous space is exclusively composed of fibrin. There are no additions of collagen to be found. Therefore, it appears unjustified to use the term "fibrinoid". Glycosaminoglycanes are present in the stroma of villi, and they are oriented in the direction of disposition of collagenous fibers. Their content in the stroma of villi decreases with the progress of gravidity. They are also involved in displacental material transport, although the degree of involvement decreases with the progress of gravidity. Functionally, they show what has been called a "molecular screening effect". The lipid-protein system of the epithelial basement membrane-together with the endothelial basement membrane of fetal vessels in the second half of gravidity-is the principal barrier to the passive passage there-through of substances.