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Gastrulation - Anatomy & Physiology (view source)
Revision as of 14:53, 25 August 2008
, 14:53, 25 August 2008no edit summary
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**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.