noun, plural pla·cen·tas, pla·cen·tae [pluhsen-tee] /pləˈsɛn ti/.

  1. Anatomy, Zoology. the organ in most mammals, formed in the lining of the uterus by the union of the uterine mucous membrane with the membranes of the fetus, that provides for the nourishment of the fetus and the elimination of its waste products.
  2. Botany.
    1. the part of the ovary of flowering plants that bears the ovules.
    2. (in ferns and related plants) the tissue giving rise to sporangia.


  1. (esp of animals) having a placentaplacental mammals See also eutherian

noun plural -tas or -tae (-tiː)

  1. the vascular organ formed in the uterus during pregnancy, consisting of both maternal and embryonic tissues and providing oxygen and nutrients for the fetus and transfer of waste products from the fetal to the maternal blood circulationSee also afterbirth
  2. the corresponding organ or part in certain mammals
  3. botany
    1. the part of the ovary of flowering plants to which the ovules are attached
    2. the mass of tissue in nonflowering plants that bears the sporangia or spores

adj.1808, from Modern Latin placentalis, from placenta (see placenta). n.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. n. pl. pla•cen•tas

  1. 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.

  1. The sac-shaped organ that attaches the embryo or fetus to the uterus during pregnancy in most mammals. Blood flows between mother and fetus through the placenta, supplying oxygen and nutrients to the fetus and carrying away fetal waste products. The placenta is expelled after birth.
  2. The part of the ovary of a flowering plant to which the ovules are attached. In a green pepper, for example, the whitish tissue to which the seeds are attached is the placenta.

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.

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