Whole Extraembryonic

The extraembryonic coelom (c. extraembryonale; synonym exocoelom) is the primary body cavity of the embryo of vertebrates, which is formed outside the embryo.

The extraembryonic coelom appears in the early stages of embryonic development as a result of the splitting of the blastocyst into 2 layers - the epiblast and the hypoblast. Between these layers a cavity is formed, which is called the extraembryonic coelom. It surrounds the embryo and is lined with epithelium derived from the trophectoderm of the blastocyst.

In vertebrates, the extraembryonic coelom subsequently undergoes changes and gives rise to a number of extraembryonic structures, such as the yolk sac, amnion, chorion and allantois. These structures perform important functions in ensuring the normal development of the embryo.

Thus, the extraembryonic coelom plays a key role in the early stages of vertebrate embryogenesis, forming peri-embryonic membranes and organs necessary to maintain favorable conditions for embryo development.

The extraembryonic coelomia is the gastrula from which the coelomia is formed in various animals. Extraembryonic coelomia, or exocelomia (from the Greek exo - outside and coelomia) is absent in cyclostomes (lamreys and hagfish), fish, amphibians, reptiles, birds, and mammals. Cavity worms are classified as coelomic. There are also a number of unclear issues regarding insect coelomia.