An embryonic disc is a flattened, plate like structure in the early embryo.
The embryonic disc in the early embryo is initially two layered also called bilaminar and later the embryonic disc becomes three layered also known as trilaminar.
The embryonic disc is formed from the inner cell mass, from which the actual fetus develops, differentiating into all the body's tissues and organs.
An embryonic disc sits between the amniotic cavity above and the yolk sac below, with the top layer called the epiblast giving rise to the embryo proper, and the lower layer called the hypoblast forming the yolk sac.
The key stages and layers of the embryonic disc are the bilaminar disc, in week 2, which is formed by the inner cell mass into 2 layers.
The epiblast or upper, which is the columnar cells that will form the embryo.
And the hypoblast or lower, which is the cuboidal cells forming the primitive yolk sac.
In week 3, gastrulation occurs, in which the epiblast folds inwards and creates a third layer also known as mesoderm and forms the trilaminar disc.
Then the trilaminar disc, which is 3 layers, is the ectoderm from the epiblast, which becomes skin, brain and nervous system.
Mesoderm, the new layer, which forms muscles, skeleton, circulatory system, etc.
And the endoderm, from the epiblast/hypoblast, develops into the lining of the gut, lungs and other organs.
The significance of the embryonic disc is the foundation, orientation and folding.
The embryonic disc is the source of all cells for the developing organism.
The formation of the primitive streak on the disc establishes the body's head to tail axis.
And the embryonic disc also undergoes folding to create the 3 dimensional body plan of the embryo, forming the anterior body all and gut tube.