Article révisé par les pairs
| Résumé : | The histophysiology varies in the three different types of placenta, namely the epitheliochorial, the endotheliochorial, and the haemochorial. The histophysiology of epitheliochorial placentas is almost unknown. In the case of the other two types, researches have been made which, although fragmentary, allow of the following conclusions being deduced. In endotheliochorial placentas the hypertrophied uterine glands contribute considerably to the nutrition of the embryo. The remainder of the substances, at the expense of which embryonic development is carried out, come from the maternal blood and are absorbed in the region of the placenta by the trophoblastic ectoderm. This absorption is selective: when certain soluble substances are injected into the maternal circulation, some are seen to pass into the embryo, others are stopped by the trophoblast, in which they accumulate. In the case of haemochorial placentas the uterine glands supply little material for embryonic development. The embryotrophic substances are derived from two sources. One of these is the maternal cells, which become filled with reserve inclusions (decidual cells) and are absorbed by the trophoblast. A veritable maternal placenta is thus formed, which, in certain species, can change its situation in the course of gestation, being at first localised in the basilar deciduum, then rapidly absorbed, and finally reformed in the region of the mesometrium. The second source is the maternal blood which directly bathes the foetal trophoblast. The latter partially fixes colouring matters injected into the mother, while allowing a certain amount to diffuse into the embryonic mesenchymatous tissue of the placenta. Here the maternal blood, comes into contact with the embryonic vessels, the endothelium of which acts as an impassable barrier for the dyes, since these are not found in the embryo itself, although they pass into the external coelom. In rodents the umbilical vesicle, by means of its vitelline endoderm, acts as an energetic resorber and contributes to the nutrition of the embryo. In the rodents showing inversion of layers the endoderm of the umbilical vesicle is differentiated differently on the placental face and on the inner layer of the umbilical vesicle. Physiological differences correspond to these morphological differences. Copyright © 1930, Wiley Blackwell. All rights reserved |
