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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



(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 outermost of the extraembryonic membranes of amniotes, enclosing the embryo and all of its other membranes.
References in periodicals archive ?
In the current study, the researchers prospectively examined chorion membrane samples to identify a pattern of bacterial presence and association with chorion thinning.
Our results suggest that insecticides, specifically bifenthrin, beta-cyfluthrin, and beta-cyfluthrin + acephate, may have the ability to penetrate the chorion of southern green stink bug egg masses.
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.
It is tremendously exciting to see such a respected and energetic team bring their experience to the incomparable properties we represent," says Diana Manson, Chorion Silver Lining's Executive Vice President of Creative.
Hit Entertainment said it had undertaken due diligence on Chorion, but decided against continuing discussions with the company's board.
The surface morphology and chorion of insect eggs has been intensively studied by scanning and transmission electron microscope.
Noddy will begin appearing on Japanese satellite channels Kids Station and BS Fuji and national digital station Megaport Broadcasting in the second half of 2005, Chorion said.
Fertilized Medaka eggs were viewed under light microscopy through the transparent chorion from approximately six hours post-fertilization until hatching eleven days later.
If the twins share a chorion, they also share a placenta.
NEW YORK -- Chorion, the global media content group, announces results for the year to 31 March 2010.