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Gastrulation - Anatomy & Physiology (view source)
Revision as of 14:01, 25 August 2008
, 14:01, 25 August 2008no edit summary
*Cells in the primitive groove change shape from columnar to wedge shaped, which produces two elevations either side of a groove.
*Cells in the primitive groove change shape from columnar to wedge shaped, which produces two elevations either side of a groove.
*Epiblastic cells of the primitive streak begin to ingress ventrally to form the new germ layers.
*Epiblastic cells of the primitive streak begin to ingress ventrally to form the new germ layers.
**As the primitive streak extends into the anterior it enters certain "territories" of the epiblast. These are regions, organised from posterior to anterior, which are destined to become certain germ layers.
===Endodermal Ingression===
*Cells of the prospective endoderm are the first to ingress.
**Ingression involves the breaking of attachments with neighbouring cells of the epiblast and moving ventrally.
*Cells that have broken free of the epiblast make an epithelial to mesenchymal transition.
**This is achieved by breaking of the basal lamina, followed by breaking of intercellular connections. Cells undergoing this transition change from being regularly shaped to being irregularly shaped.
*When the cells reach the hypoblast, they interchalate with cells of the hypoblast and revert back to their original
epithelial state.
===Mesodermal Ingression===
*As the streak elongates it enters the prospective lateral plate mesoderm (LPM) region of the epiblast.
*Cells of the prospective LPM converge and ingress, making an epithelial to mesenchymal transition.
*They do not interchalate with the endoderm, but '''remain mesenchymal'''.
**They then migrate laterally and anteriorly.
*As the streak extends further, it enters the intermediate and paraxial mesoderm territories, which ingress in a similar fashion.
*Cells of the LPM are most lateral, then intermediate followed by paraxial mesoderm and axial mesoderm.
*As ingression continues, the hypoblast is pushed laterally as the endoderm spreads.