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Gastrulation - Anatomy & Physiology (view source)
Revision as of 14:53, 25 August 2008
, 14:53, 25 August 2008no edit summary
**They then migrate laterally and anteriorly.
**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.
*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.
*Cells of the LPM are most lateral, then intermediate followed by paraxial mesoderm.
*As ingression continues, the hypoblast is pushed laterally as the endoderm spreads.
*As ingression continues and the endoderm continues to interchalate, the hypoblast is pushed laterally.
==Gastrulation at the Node==
*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.
**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.
***The node then regresses posteriorly, destroying the primitive streak and forming the '''notochord''' (axial mesoderm).
***The notochord begins at the level of the midbrain.
****Anterior cells are developing before posterior cells have even undergone gastrulation.
==Gastrulation at the Tail Bud==
*Cells at the posterior of the primitive streak are allocated to form the tail bud. When the primitive streak elongates, these cells don't follow, but migrate posteriorly and form a condensed ball of cells called the tail bud.
*The tail bud exists to form cells of the hindlimb.
*Tail notochord and somites form through regression of the tail bud.
**'''No endoderm exists in the tail bud.'''
*Without the tail bud, the notochord would run out of cells before the hindlimb could be made.
*In animals that have tails, cells at an additional site undergo gastrulation.