placenta /pla·cen·ta/ (plah-sen´tah) pl. placentas, placen´tae [L.] an organ characteristic of true mammals during pregnancy, joining mother and fetus, providing endocrine secretion and selective exchange of soluble bloodborne substances through apposition of uterine and trophoblastic vascularized parts.placen´tal
placenta accre´ta one abnormally adherent to the myometrium, with partial or complete absence of the decidua basalis.
circumvallate placenta one in which a dense peripheral ring is raised from the surface and the attached membranes are doubled back over the placental edge.
deciduate placenta , deciduous placenta a placenta or type of placentation in which the decidua or maternal parts of the placenta separate from the uterus and are cast off together with the trophoblastic parts.
fetal placenta the part of the placenta derived from the chorionic sac that encloses the embryo, consisting of a chorionic plate and villi.
hemochorial placenta one in which maternal blood comes in direct contact with the chorion, as in humans.
placenta incre´ta placenta accreta with penetration of the myometrium.
maternal placenta the maternally contributed part of the placenta, derived from the decidua basalis.
placenta membrana´cea one that is abnormally thin and spread out over an unusually large area of the uterine wall.
placenta percre´ta placenta accreta with invasion of the myometrium to its peritoneal covering, sometimes causing rupture of the uterus.
placenta pre´via one located in the lower uterine segment, so that it partially or completely covers or adjoins the internal os.
placenta spu´ria an accessory portion having no blood vessel attachment to the main placenta.
placenta succenturia´ta , succenturiate placenta an accessory portion attached to the main placenta by an artery or vein.
villous placenta one characterized by the presence of villi that are outgrowths of the chorion.
placenta spu·ri·a (spy r  - )n. A mass of placental tissue that has no vascular connection with the main placenta. |
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