Changes

==Introduction==

==Introduction==

Gastrulation is the process of forming the three germ layers; '''ectoderm''', '''mesoderm''' and '''endoderm'''. It is achieved through a series of highly coordinated series of cell movements. Cells that will form the endodermal and mesodermal organs are brought inside the embryo, whilst cells that will form ectoderm move to spread out over the outside of the embryo.

Gastrulation is the process of forming the three germ layers; '''ectoderm''', '''mesoderm''' and '''endoderm'''. It is achieved through a series of highly coordinated cell movements. Cells that will form the endodermal and mesodermal organs are brought inside the embryo, whilst cells that will form ectoderm move to spread out over the outside of the embryo.

'''Ectoderm''' - outside layer

'''Ectoderm''' - outside layer

'''Endoderm''' - inner layer

'''Endoderm''' - inner layer

==Mechanism of Gastrulation==

==Mechanism of Gastrulation==

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:

When the embryo is in its 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 is a circular plate of cells that ingress ventrally to give 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. In gastrulation, cells ingress ventrally from the epiblast to form the three germ layers. Gastrulation occurs at three embryonic sites:

1.'''Primitive Streak'''

1.'''Primitive Streak'''