Changes

==Mechanism of Gastrulation==

==Mechanism of Gastrulation==

*When the embryo is in it's blastula stage it has two cell layers; the epiblast and hypoblast.

When the embryo is in it's blastula stage it has two cell layers; the epiblast and hypoblast. The '''epiblast''' is columnar, whilst the '''hypoblast''' is cuboidal. Each is a single cell thick. The epiblast gives rise to all three cell layers; the hypoblast makes no contribution. The endoderm and mesoderm develop by proliferation and migration of cells of the epiblast, what remains of the epiblast forms the ectoderm. The epiblast is a circular plate of cells. In gastrulation, cells ingress ventrally from the epiblast to form the three germ layers. Gastrulation occurs at three embryonic sites:

**The epiblast is columnar whilst the hypoblast is cuboidal - each is a single cell thick.  

 

*'''The epiblast gives rise to all three cell layers; the hypoblast makes no contribution'''.  

1.'''Primitive Streak'''

*The endoderm and mesoderm develop by proliferation and migration of cells of the epiblast.

 

**What remains of the epiblast forms the ectoderm.

2.'''Node'''

*The epiblast is a circular plate of cells. In gastrulation, cells ingress ventrally from the epiblast to form the three germ layers.  

 

*Gastrulation occurs at three embryonic sites:

3.'''Tail Bud'''

::'''Primitive Streak'''

::'''Node'''

::'''Tail Bud'''

==Gastrulation at the Primitive Streak==

==Gastrulation at the Primitive Streak==