haemochorial
Haemochorial, also spelled hemochorial, describes a type of placentation in which the chorion (fetal tissue) is in direct contact with maternal blood within the intervillous space, with only trophoblastic tissue separating the two circulations. In this arrangement the maternal epithelium and much of the decidua are breached by placental invasion, enabling close exchange between the maternal and fetal blood.
This placentation type occurs in humans and many other primates, as well as several rodent species, and
Functionally, haemochorial placentation supports efficient transfer of gases, nutrients, and wastes between mother and fetus. The
Compared with epitheliochorial placentation, where maternal tissues largely remain intact and the barrier is thicker, haemochorial