extraembryonic mesoderm

It is derived from extraembryonic mesoderm.

Between days 13 and 15, the proliferation of extraembryonic mesoderm, primitive streak and embryonic mesoderm take place.

When the extraembryonic mesoderm is separated into two portions, a new gap arises called the chorionic cavity, or the extra-embryonic coelom.

It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes.

As development progresses, small lacunae begin to form within the extraembryonic mesoderm which become larger and form the extraembryonic coelom.

While the primary yolk sac is forming, extraembryonic mesoderm makes its way into the blastocyst cavity to fill it with loosely packed cells.

When day 13 rolls around, the connecting stalk, a dense portion of extraembryonic mesoderm, restrains the embryonic disc in the chorionic cavity.

After that, the epiblast and the hypoblast establish contact with the extraembryonic mesoderm until they cover the yolk sac and amnion.

When the extraembryonic mesoderm splits into two layers, the amnion, yolk sac, and chorion follow its lead and also become double layered.

In the yolk sac's blood islands, HPCs and EC lineages emerge from the extraembryonic mesoderm in near unison.

Cells from the yolk sac endoderm form a layer of connective tissue, the extraembryonic mesoderm, which surrounds the amnion and yolk sac.

Cells of the epiblast migrate along the outer edges of this reticulum and form the extraembryonic mesoderm, which makes it difficult to maintain the extraembryonic reticulum.

The intraembryonic coelom is lined by somatic and splanchnic lateral plate mesoderm, while the extraembryonic coelom is lined by extraembryonic mesoderm.

Formation of the definitive yolk sac happens after the extraembryonic mesoderm splits, and it becomes a double layered structure with hypoblast-derived endoderm on the inside and mesoderm surrounding the outside.

Other cells migrate through the caudal part of the primitive line and form the lateral mesoderm, and those cells migrating by the most caudal part contribute to the extraembryonic mesoderm.

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.

The pluriblast is a pluripotent population of cells in the early mammalian conceptus that is distinct from the trophoblast, and gives rise to the germ layers of the embryo proper, as well as extraembryonic endoderm and extraembryonic mesoderm.

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.