ABSTRACT
Implantation of the embryo in the uterus and development of a placental connection to the maternal circulation is a strong evolutionary advantage of eutherian mammals over oviparous animals. The placenta and
embryonic/fetal membranes (amnion, chorion, and allantois) form the interface between the microcirculatory systems of the mother and embryo, function for efficient sustained exchange of nutrients, respiratory gases, and metabolic waste, protect the growing embryo/fetus, and are a source of hormones. The
Synopsis
Background
• Embryos of some species, including primates and rodents, are invasive and penetrate the epithelial layer of the endometrium.
