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placenta |
Also found in: Dictionary/thesaurus, Medical, Wikipedia, Hutchinson | 0.07 sec. |
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placenta (pləsĕn`tə) or afterbirth, organ that develops in the uterus during pregnancy. It is a unique characteristic of the higher (or placental) mammals. In humans it is a thick mass, about 7 in. (18 cm) in diameter, liberally supplied with blood vessels. The placenta is attached to the uterus, and the fetus is connected to the placenta by the umbilical cord. The placenta draws nourishment and oxygen, which it supplies to the fetus, from the maternal circulation. In turn, the placenta receives the wastes of fetal metabolism and discharges them into the maternal circulation for disposal. It also acts as an endocrine gland, producing estrogen, progesterone, and gonadotrophin. Shortly after delivery of the fetus the placenta is forced out by contractions of the uterus. Severe hemorrhage may occur if the placenta does not emerge in its entirety or if the uterus fails to contract properly. placentaOrgan in most mammals that develops in the uterus along with a fetus to mediate metabolic exchange. The umbilical cord attaches it to the fetus at the navel. Nutrients and oxygen in the mother's blood pass across the placenta to the fetus, and metabolic wastes and carbon dioxide from the fetus cross in the other direction; the two blood supplies do not mix. Other substances (e.g., alcohol or drugs) in the mother's blood can also cross the placenta, with effects including congenital disorders and drug addiction in the newborn (see fetal alcohol syndrome); some microorganisms can cross it to infect the fetus, but so do the mother's antibodies. The placenta, weighing a pound or more at the end of pregnancy, is expelled at parturition. Some animals eat it as a source of nutrients; in some species this stimulates lactation. placenta 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 circulation 2. the corresponding organ or part in certain mammals 3. Botany a. the part of the ovary of flowering plants to which the ovules are attached b. the mass of tissue in nonflowering plants that bears the sporangia or spores How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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Whereas the proportion of women experiencing placenta previa (implantation of the placenta close to or over the opening to the birth canal) increased steadily with age, the proportion experiencing placental abruption (separation of the placenta from the uterus) was relatively high at the extreme ages but dropped among women in their 20s and early 30s; a similar pattern was found in rates of fetal abnormality. Researchers are developing new ways to harvest babies' genes in less risky ways--for example, from fetal DNA floating in a mother's blood or from cells that have detached from the placenta and lodged in her cervix. Rodriguez found a new niche in the mid-1990s in hair products aimed at Latinos, namely styling gel and shampoo enriched by sheep placenta (a common ingredient in Latino shampoos). |
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