Expansion of placental site and maternal blood supply of primate placentas.

Abstract

AbstractDevelopment of placental site and uteroplacental arteries was studied in Tarsiidae, Ceboidea, Cercopithecoidea, and Hominoidea. In Tarsiidae the placental attachment and single artery remain essentially unchanged from early on, and the placenta grows beyond the original site in the shape of a button. In Tarsiidae and Ceboidea maternal arteries and their branches are incorporated in the placenta and their wall is replaced later by a layer of fibrin, Ceboidea have several arteries in the original placental site; this site is enlarged including additional arteries by ingrowth of villi from the chorion in an area surrounding the original site. Further growth is by centrifugal spread; the basal endometrium is stretched and no new arteries are tapped. In Cercopithecoidea the placenta has a sharp border from early on. Spread with stretching of the underlying endometrium occurs here, too. Additional arteries running in this stretched endometrium are secondarily tapped and increase the total number. The disc of Hominoidea, remaining after formation of the chorion laeve, also stretches the underlying decidua, but then trophoblast pervades much of it until it taps arteries in a much larger area than in the other forms.