Gastrulation. Hypoblast forms endoderm. And contains material for gut, forms roof of yolk sac!

Gastrulation

- this is the stage of embryogenesis resulting in the formation of germ layers (ectoderm, mesoderm and endoderm)and a complex of axial organs (neural tube, notochord, gut)

In humans gastrulation occurs in two stages:

1. Delamination

2 Immigration

Delamination begins on the 7th day of embryonic development and is translated as splitting or stratification. At this stage the embryoblast splits into two plates: epiblast (upper) and hypoblast (lower)!

Ectoderm is formed from the epiblast
Epiblast also contains material for neural tube, mesoderm, notochord and form bottom of amnion!

Hypoblast forms endoderm. And contains material for gut, forms roof of yolk sac!

As a result of delamination the embryo becomes two-layerand looks as bilaminar disk!

Immigration begins on the 14-15th day, this is the process of moving cells from the epiblast into the narrow space between the epiblast and the hypoblast. In this case, a primitive streak is formed, and from it the mesoderm is formed. At the cranial end of the primitive streak, a thickening forms - the Hensen's nodule is the predecessor of the notochord. As a result of immigration, the embryo becomes three-layered amd looks as 3-laminar disk!

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