Establishment of The Amniotic Cavity
Beginning on day 8, the amniotic cavity is the first new cavity to form during the second week of development. Fluid collects between the epiblast and the trophoblast, which splits the epiblast into two portions. The layer at the embryonic pole grows around the amniotic cavity, creating a barrier from the cytotrophoblast. This becomes known as the amnion, which is one of the four extraembyonic membranes and the cells it comprises are referred to as amnioblasts. Although, the amniotic cavity starts off small it eventually grows to be larger than the blastocyst and by week 8, the whole embryo is encompassed by the amnion.
Read more about this topic: Bilaminar Blastocyst
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