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Related to Chorion: chorion laeve, chorion frondosum


The outermost of the several extraembryonic membranes in amniotes (reptiles, birds, and mammals) enclosing the embryo and all of its other membranes. The chorion, or serosa, is composed of an outer layer of ectodermal cells and an inner layer of mesodermal cells, collectively the somatopleure. Both layers are continuous with the corresponding tissue of the embryo. The chorion arises in conjunction with the amnion, another membrane that forms the outer limb of the somatopleure which folds up over the embryo in reptiles, birds, and some mammals. The chorion is separated from the amnion and yolk sac by a fluid-filled space, the extraembryonic coelom, or body cavity. In those mammals in which the amnion forms by a process of cavitation in a mass of cells, instead of by folding, the chorion forms directly from the trophoblastic capsule, the extraembryonic ectoderm, which becomes gradually underlain by extraembryonic mesoderm.

In reptiles and birds the chorion fuses with another extraembryonic membrane, the allantois, to form the chorioallantois, which lies directly below the shell membranes. An extensive system of blood vessels develops in the mesoderm of this compound membrane which serves as the primary respiratory and excretory organ for gaseous interchanges. In all mammals above the marsupials, the chorion develops special fingerlike processes (chorionic villi) extending outward from its surface. To a varying degree in different species of mammals, the villous regions of the chorion come into more or less intimate contact with the uterine mucosa, or uterine lining, of the mother, thereby forming the various placental types. See Allantois, Amniota, Fetal membrane, Germ layers

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(1) The outermost embryonic membrane of birds, reptiles, and mammals (including human beings) that is formed in the early stages of development; also called serosa. The embryo receives oxygen from the environment through the chorion, and the embryo of mammals also receives food and eliminates metabolites and carbon dioxide through the membrane.

In birds and reptiles, the chorion fuses with the allantois to form a common chorioallantoic membrane next to the eggshell. The chorion of mammals, including humans, is covered with villi, into which the blood vessels of the embryo grow. The villi penetrate into the uterine wall, where they form the placenta.

(2) A secondary eggshell of invertebrates and some lower vertebrates.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The outermost of the extraembryonic membranes of amniotes, enclosing the embryo and all of its other membranes.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The pharmaceutical consortium's studies also did not resolve important questions surrounding the presence of the chorion. For example, the uptake studies were generated almost exclusively from pharmaceuticals (17/20 chemicals), raising the question of whether the results are valid for other types of chemicals.
Among all subjects, bacterial counts were inversely correlated with chorion thinning: the more bacteria present, the thinner the chorion.
Continued research into what processes permit the diffusion of insecticides into the chorion of stink bug eggs and if spray additives such as crop oil concentrate will assist in insecticide delivery are needed.
occulta, that hatches from its chorion before metamorphosis, in an anterior-to-posterior manner.
Chorion senior brand manager Esra Cafer, said: "We are thrilled that Beatrix Potter's wonderful characters can now be enjoyed in this innovative format by visually impaired and blind people.
Chorion said the new Noddy in Toyland show went straight to the No 1 spot for four to six-year-old viewers on Five in its first month.
Executive chairman Lord Alli said he wanted to issue the figures in the wake of the collapse of Entertainment Rights, to show Chorion were not in similar trouble.
At approximately 7 days after ovulation the chorion (trophectoderm) of the developing embryo begins producing chorionic gonadotropin.
thanks to such assets as "Noddy" and the Agatha Christie estate, Chorion (whose name, pronounced corey-on, derives from a medical term for the membrane surrounding an embryo) is making inroads in the U.S.
Hit Entertainment said it had undertaken due diligence on Chorion, but decided against continuing discussions with the company's board.
The morphological characteristics of eggs, especially the surface of chorion, show distinct differentiation and ootaxanomic significance in various insect orders (Hinton 1981; Salkeld 1983; Margaritis 1985; Gaino and others 1987; Sahlen 1996; Candan 1997).
Entertainment rights group Chorion said it had agreed a deal with Japanese intellectual property firm OLC/Rights Entertainment Japan to distribute its Make Way for Noddy TV series to three major Japanese TV networks.