| PP | diphosphate group; emphysema [pink puffers]; near point of accommodation [Lat. punctum proximum]; pa... |
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| annular placenta | A placenta in the form of a band encircling the interior of the uterus. Synonym: zonary placenta. (05 Mar 2000) |
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| battledore placenta | A placenta in which the umbilical cord is attached at the border; so-called because of the fancied resemblance to the racquet (racket) used in battledore, a precursor to badminton. (05 Mar 2000) |
| bidiscoidal placenta | A placenta with two separate disc-shaped portions attached to opposite walls of the uterus, normal for certain monkeys and shrews, and occasionally found in humans. (05 Mar 2000) |
| margination of placenta | See: placenta marginata. (05 Mar 2000) |
| maternal placenta | <anatomy> The part of the placenta derived from the uterine tissue. See: placenta. Synonym: maternal placenta, placenta uterina. (05 Mar 2000) |
| villous placenta | A placenta in which the chorion forms villi. (05 Mar 2000) |
| central placenta previa | Placenta previa in which the placenta entirely covers the internal os of the cervix. Synonym: central placenta previa, total placenta previa. (05 Mar 2000) |
| retained placenta | Incomplete separation of the placenta and its failure to be expelled at the usual time after delivery of the child. Synonym: incarcerated placenta. (05 Mar 2000) |
| chorioallantoic placenta | A placenta (such as that of primates) in which the chorion is formed by the fusion of the allantoic mesoderm and vessels to the inner face of the serosa. (05 Mar 2000) |
| chorioamnionic placenta | A form of placentation in which the amnion is fused to the inside of the chorion, thus permitting interchange of water and electrolytes between mother and foetus. (05 Mar 2000) |
| choriovitelline placenta | A placenta (seen in some lower animals) in which the chorion is formed by the fusion of yolk-sac mesoderm and vessels to the inner face of the serosa. (05 Mar 2000) |
| monochorionic diamniotic placenta | The placenta(s) of a twin pregnancy; if dizygotic, the placenta's may be separate or fused, the latter retaining two amniotic and two chorionic sacs (dichorionic diamniotic placenta); if monozygotic, the placenta may be a (05 Mar 2000) |
| monochorionic monoamniotic placenta | Depending on the stage at which twinning took place; if twinning occurs early, there may be a fused placenta with two chorionic and two amniotic membranes. Alternative form: monochorionic diamniotic placenta (05 Mar 2000) |
| placenta | <anatomy, obstetrics> An organ characteristic of true mammals during pregnancy, joining mother and offspring, providing endocrine secretion and selective exchange of soluble, but not particulate, blood borne substances through an apposition of uterine and trophoblastic vascularised parts. According to species, the area of vascular apposition may be diffuse, cotyledonary, zonary or discoid, the nature of apposition may be labyrinthine or villous, the intimacy of apposition may vary according to what layers are lost of those originally interposed between maternal and foetal blood (maternal endothelium, uterine connective tissue, uterine epithelium, chorion, extraembryonic mesoderm and endothelium of villous capillary). The chorion may be joined by and receive blood vessels from either the yolk sac or the allantois and the uterine lining may be largely shed with the chorion at birth (deciduate) or may separate from the chorion and remain (nondeciduate). The human placenta is discoid, villous, haemochorial, chorioallantoic and deciduate. After birth, it weighs about 600 gm. And is about 16 cm. In diameter and 2 cm. Thick, discounting a principal functional part, the maternal blood in the intervillous space (which leaks out at birth) into which the chorionic villi dip. The villi are grouped into adjoining cotyledons making about 20 velvety bumps on the side of the placenta facing outward to the uterus, the inner side of the placenta facing the foetus is smooth, being covered with amnion, a thin avascular layer that continues past the edges of the placenta to line the entire hollow sphere of chorion except where it is reflected to cover the umbilical cord, which joins foetus and placenta. The cord usually joins the placenta near the centre but may insert at the edge, on the nonplacental chorion or on an accessory placenta. (31 Dec 1997) |
| placenta, accessory | An extra placenta separate from the main placenta. Also called a succenturiate or supernumerary placenta. Placenta accreta: the abnormal adherence of the chorionic villi to the myometrium. The vascular processes of the chorion (a foetal membrane that enters into the formation of the placenta) grow directly in the myometrium (the muscular portion of the uterus). Normally there is tissue intervening between the chorionic villi and the myometrium. Here there is not. The word accreta comes from the latin accretio from ad meaning to or toward + crescere meaning to grow. Placenta accreta can progress to placenta percreta. (12 Dec 1998) |