Placenta

Placenta, specialized structure derived from the uterus lining and part of the embryo after implantation. It separates and yet ensures a close and extensive contact between the maternal (uterine) and fetal (umbilical) blood circulations. This allows nutrients and oxygen to pass from the mother to the fetus, and waste products to pass in the reverse direction. Gonadotropins produced by the placenta prepare the maternal body for delivery and the breasts for lactation. The placenta is delivered after the child at birth (the afterbirth) by separation of the blood-vessel layers.

See also: Reproduction.