Chorion

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Related to chorions: chorion frondosum, chorion laeve

Chorion

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

Chorion

 

(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.

chorion

[′kȯr·ē·än]
(embryology)
The outermost of the extraembryonic membranes of amniotes, enclosing the embryo and all of its other membranes.
References in periodicals archive ?
All nymphs eventually positioned themselves adjacent to the chorions, facing them.
meditabunda, immediately following emergence from the eggs, visit several eggs/chorions and spend a relatively large amount of time on top of each one before moving off to the side and settling into their final position adjacent the chorions.
At 5 weeks of pregnancy one should be able to see a sonolucent gestational sac, representing the chorion, on transvaginal ultrasound.
At that point in monochorionic-diamniotic pregnancies, the amnion is a thin sonolucent line within the chorion.
Women with preterm premature rupture of membranes [PROM] may have a chronic inflammatory response that leads to cell death in the chorion and preterm labor," suggested Dr.
Chorion is a media content company that owns and manages an extensive portfolio of classic and contemporary premium copyrights with worldwide appeal.