Later, the degeneration of Reichert’s membrane leaves the visceral yolk sac exposed as an extensive bounding barrier and fluid exchange may occur here, as well as at the placenta. The fluid content of the normal exocelomic plus amniotic cavities is influenced by conceptus genotype, and the volume is normally greatest at E16.5 : the volume is under physiological regulation, and it is nearly halved by treatment of the mother with corticoids. birth control yasmin
When Igf2 gene activity is absent from the whole con-ceptus or the derivatives of either component of the blastocyst, then there are major reductions in the volume bounded by the visceral yolk sac at E16.5 (Tables 1 and 3). The reduced fluid volume of the exocelomic and amniotic cavities may provide another example of IGF-2 control of fluid content, for the volume of these cavities is enlarged when IGF-2 levels are unusually high (see Introduction). Our primary conclusion is that IGF-2 deficiency reduces fluid transport from the mother or fluid retention by the conceptus. The ICM derivatives have a major influence on these processes because IGF-2 deficiency in the ICM causes a decrease in fluid volume similar to that caused by IGF-2 deficiency in the whole conceptus (compare Tables 1 and 3).