File:Stage7 cloacal-oral-membranes.jpg

From Embryology

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Carnegie Stages 7 showing approximate regions where buccopharyngeal and cloacal membranes would lie on the embryonic disc.

  • top dot - buccopharyngeal membrane
  • middle dot - primitive node
  • bottom dot - cloacal membrane
  • grey line - primitive streak
Features: embryonic disc, primitive node, primative streak, primative groove, yolk sac

Facts: Week 3, 15 - 17 days, 0.4 mm

View 1: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.

Stage 7 Labelled | Stage 7 Molecular | Stage 7 SEM | Stage 8

Events: Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm.

Mesoderm lies between the ectoderm and endoderm as a continuous sheet except at the buccopharyngeal and cloacal membranes. These membranes have ectoderm and endoderm only and will lie at the rostral (head) and caudal (tail) of the gastrointestinal tract.

From the primitive node a tube extends under the ectoderm in the opposite direction to the primitive streak. This tube forms first the axial process then notochordal process, then finally the notochord.

The notochord is a key to embryonic folding and regulation of ectoderm and mesoderm differentiation. It lies in the rostrocordal axis and the embryonic disc will fold either side ventrally, pinching off a portion of the yolk sac to form the lining of the gastrointestinal tract.

Stage 7 Links: :Carnegie stage 7 | Gastrulation | Mesoderm

Reference

Image Source: UNSW Embryology

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current12:15, 10 August 2009Thumbnail for version as of 12:15, 10 August 2009690 × 800 (70 KB)MarkHill (talk | contribs)Carnegie Stages 7 showing approximate regions where buccopharyngeal and cloacal membranes would lie on the embryonic disc. Features: embryonic disc, primitive node, primative streak, primative groove, yolk sac Facts: Week 3, 15 - 17 days, 0.4 mm View 1