Extra-embryonic coelom

Extraembryonic coelom
The extraembryonic coelom (or chorionic cavity) is shown between the two layers of extraembryonic mesoderm (labelled "mes.") in this image of an implanted embryo.
Latin	coeloma extraembryonicum, cavitas chorionica
Carnegie stage	6a
Days	12
Precursor	Heuser's membrane
Code	TE E5.8.0.0.1.0.1

The extraembryonic coelom (or Chorionic cavity)^[1] is a portion of the conceptus consisting of a cavity between Heuser's membrane and the Trophoblast.

During formation of the primitive yolk sac, some of the migrating Hypoblast cells transdifferentiate into mesenchymal cells that fill the space between Heuser's membrane and the Trophoblast, forming the extraembryonic mesoderm . As development progresses, small lacunae begin to form within the extraembryonic mesoderm which become larger and form the extraembryonic coelom.

It divides the extraembryonic mesoderm into two layers: extraembryonic splanchnopleuric mesoderm, which lies adjacent to Heuser's membrane around the outside of the primitive yolk sac, and extraembryonic somatopleuric mesoderm, which lies adjacent to the cytotrophoblast layer of the embryo.

The extraembryonic coelemic cavity is also called the chorionic cavity, and is enclosed by the chorionic plate, which is composed of an inner layer of somatopleuric mesoderm and an outer layer of trophoblast cells.

References

1. ^ week2

External links

• http://isc.temple.edu/marino/embryology/EMBI97/img015.GIF
• http://www.embryology.ch/anglais/hdisqueembry/triderm09.html
• http://sprojects.mmi.mcgill.ca/embryology/earlydev/week2/eemes&coel.html

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