placentation

plac·en·ta·tion

P0343000 (plăs′ən-tā′shən)n.1. a. Formation of a placenta in the uterus.b. The type or structure of a placenta.2. Botany Arrangement of placentas within the ovary.

placentation

(ˌplæsɛnˈteɪʃən) n1. (Botany) botany the way in which ovules are attached in the ovary2. (Zoology) zoology a. the way in which the placenta is attached in the uterusb. the process of formation of the placenta

Thesaurus

Noun	1.	placentation - the formation of the placenta in the uterusbodily function, bodily process, body process, activity - an organic process that takes place in the body; "respiratory activity"
	2.	placentation - arrangement of the ovules in the placenta and of the placentas in the ovaryreproductive structure - the parts of a plant involved in its reproductionapical placentation - where one or few ovules develop at the top of a simple or compound ovaryaxile placentation - ovules are borne at or around the center of a compound ovary on an axis formed from joined septabasal placentation - where one or few ovules develop at the base of a simple or compound ovaryfree central placentation - where ovules develop on a central column in a compound ovary lacking septa or with septa at base onlylamellate placentation - with ovules on thin extensions of the placentae into a compound ovarymarginal placentation, ventral placentation - with ovules borne on the wall along the ventral suture of a simple ovaryparietal placentation - where ovules develop on the wall or slight outgrowths of the wall forming broken partitions within a compound ovary

Placentation

The intimate association or fusion of a tissue or organ of the embryonic stage of an animal to its parent for physiological exchange to promote the growth and development of the young. It enables the young, retained within the body or tissues of the mother, to respire, acquire nourishment, and eliminate wastes by bringing the bloodstreams of mother and young into close association but never into direct connection. Placentation characterizes the early development of all mammals except the egg-laying duckbill platypus and spiny anteater. It occurs in some species of all other orders of vertebrates except the birds. In fact, in certain sharks and reptiles it is almost as well developed as in mammals. A few examples are also known among invertebrates (Peripatus, certain tunicates, and insects). See Fetal membrane

Block removed from center of human placenta

Efficient interchange depends on close proximity of large areas of fetal tissues to maternal blood and glandular areas. This is provided in mammals by a remarkable regulatory cooperation between the developing outer layer (trophoblast) of the chorion, together with the vascular yolk sac or allantois or both, and the mother's uterine lining (endometrium). In the typical mammalian placenta, which is always formed by the chorion and the allantoic vessels, the fetal and maternal bloodstreams are as close as a few thousandths of a millimeter from each other (see illustration). The surface area of the fetal villi which contain the functional fetal capillaries is probably several times larger than the body surface of the female. In humans this ratio is known to be about 8:1.

Placentation

the location of the placenta in the ovary of an angiospermous plant. A distinction is made between laminar placentation, in which the placentas are located in the inner surface of the carpel (on the sides or along the midrib), and marginal placentation, in which the placentas are located near the margins of the carpel.

Syncarpous gynoecia are marked by central marginal placentation: the placentas are located near the margins of the carpel, in the corners of the locules of the ovary, and along the ovary’s longitudinal axis. Parietal marginal placentation—the disposition of the placentas on the ovary wall near the margins of the carpel—is characteristic of paracarpous gynoecia. With free central placentation the ovules are borne by a central column; this arrangement characterizes lysicarpous gynoecia. In apical and basal placentation, the placentas are located at the apex or base of the ovary, respectively. The most primitive type of placentation is laminar, with placentas scattered over the inner surfaces of the carpel.

placentation

[plas·ən′tā·shən] (botany) The attachment of ovules along the inner ovarian wall by means of the placenta. (embryology) The formation and fusion of the placenta to the uterine wall.

placentation

[plas″en-ta´shun] the series of events following implantation of the embryo and leading to development of the placenta.

plac·en·ta·tion

(plas'en-tā'shŭn), The structural organization and mode of attachment of fetal to maternal tissues in the formation of the placenta. Types of placentation are defined under placenta.

placentation

(plăs′ən-tā′shən)n.a. Formation of a placenta in the uterus.b. The type or structure of a placenta.

placentation

Obstetrics The formation of the placenta in the uterus; the process by which a placenta grows and develops in the uterus. See Extrachorial placentation.

plac·en·ta·tion

(plas'en-tā'shŭn) The structural organization and mode of attachment of fetal to maternal tissues in the formation of the placenta.

placentation

the arrangement of PLACENTAS (2) in the plant ovary, which can be classified into several categories including:

(a) apical, at the ovary apex,
(b) basal, at the ovary base,
(c) parietal, on the ovary wall,
(d) free-central, on a column growing up from the ovary base.

placentation

noun

Words related to placentation

noun the formation of the placenta in the uterus

Related Words

bodily function
bodily process
body process
activity

noun arrangement of the ovules in the placenta and of the placentas in the ovary

Related Words

reproductive structure
apical placentation
axile placentation
basal placentation
free central placentation
lamellate placentation
marginal placentation
ventral placentation
parietal placentation