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1670s of plants, 1690s of mammals, from Modern Latin placenta uterina "uterine cake" (so called 16c. by Italian anatomist Realdo Colombo), from Latin placenta "a cake, flat cake," from Greek plakoenta, accusative of plakoeis "flat," related to plax (genitive plakos) "level surface, anything flat," from PIE *plak- (1) "to be flat" (cf. Greek plakoeis "flat," Lettish plakt "to become flat," Old Norse flaga "layer of earth," Norwegian flag "open sea," Old English floh "piece of stone, fragment," Old High German fluoh "cliff"), extended form of root *pele- (2) "flat, to spread" (see plane (n.1)). So called from the shape.
placenta pla·cen·ta (plə-sěn'tə)
n. pl pla·cen·tas or pla·cen·tae (-tē)
The membranous vascular organ in female mammals that permits metabolic interchange between fetus and mother. It develops during pregnancy from the chorion of the embryo and the decidua basalis of the maternal uterus and permits the absorption of oxygen and nutritive materials into the fetal blood and the release of carbon dioxide and nitrogenous waste from it, without the direct mixing of maternal and fetal blood. It is expelled following birth.
An organ that forms in the uterus after the implantation of a zygote. The placenta moves nourishment from the mother's blood to the embryo or fetus; it also sends the embryo or fetus's waste products into the mother's blood to be disposed of by the mother's excretory system. The embryo or fetus is attached to the placenta by the umbilical cord. After birth, the placenta separates from the uterus and is pushed out of the mother's body.