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Gastrulation - Anatomy & Physiology (view source)
Revision as of 15:15, 4 September 2008
, 15:15, 4 September 2008→Gastrulation at the Node
*The primitive streak stops elongating at about 75% of the way along the length of the posterior - anterior axis.
*The primitive streak stops elongating at about 75% of the way along the length of the posterior - anterior axis.
**Cells condense at this anterior point of the primitive streak and continue to proliferate.
**Cells condense at this anterior point of the primitive streak and continue to proliferate; called '''Hensen's Node'''.
**They then ingress and replace the anterior hypoblast and form foregut endoderm.
**They then ingress and replace the anterior hypoblast and form foregut endoderm.
**Cells then migrate anteriorly, leaving the node. These cells will form all of the head mesoderm.
**Cells then migrate anteriorly, leaving the node. These cells will form all of the head mesoderm.
***The node then regresses posteriorly, destroying the primitive streak and forming the '''notochord''' (axial mesoderm).
***The node then regresses posteriorly, destroying the primitive streak and forming the '''notochord''' (axial mesoderm).
***The notochord begins at the level of the midbrain.
***The notochord begins at the level of the midbrain.
***Notochord regression also produces paraxial mesoderm.
****Anterior cells are developing before posterior cells have undergone gastrulation.
****Anterior cells are developing before posterior cells have undergone gastrulation.