embryonic disk

The embryonic disk is a crucial structure in the early development of placental mammals. It originates from the inner cell mass of the blastocyst and is the part from which the embryo itself develops. This disk-shaped group of cells lies on top of the yolk mass and typically splits into two layers: the epiblast and the hypoblast. These layers are not the definitive ectoderm and endoderm, as most of the cells forming the embryo are within the epiblast. The embryonic disk undergoes gastrulation, a process where cells move and differentiate to form the three primary germ layers (ectoderm, mesoderm, and endoderm), which will eventually give rise to all the tissues and organs of the developing organism.123