File:Stage7 notochord.jpg

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Carnegie Stage 7 showing the notochord or axial mesoderm region of the embryonic disc

  • Week 3, 15 - 17 days, 0.4 mm, embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.
  • 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 (in the centre of the embryonic disc) a tube (shown in orange) extends under the ectoderm in the opposite direction to the primitive streak (shown in grey).
  • This tube forms first the axial process then notochordal process, then finally the notochord.

Notochord

  • The notochord is a key to embryonic folding and regulation of ectoderm and mesoderm differentiation.
  • It lies in the rostrocordal axis
  • the embryonic disc will fold either side of the notochord ventrally
    • pinching off a portion of the yolk sac to form the lining of the gastrointestinal tract.
  • the embryonic disc will fold above and below the notochord ventrally
    • bringing the heart to upper abdomen
    • bringing the connecting stalk to the umbilicus
Stage 7 Mesoderm: axial | paraxial | intermediate | lateral plate

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.

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

  • Blue dot (top) - buccopharyngeal membrane
  • Blue dot (middle) - primitive node
  • Blue dot (bottom) - cloacal membrane
  • Orange line - axial mesoderm (future notochord)
  • grey line - primitive streak


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

Reference

Image Source: UNSW Embryology

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current12:21, 10 August 2009Thumbnail for version as of 12:21, 10 August 2009690 × 800 (70 KB)MarkHill (talk | contribs)Carnegie Stages 7 showing the notochord or axial mesoderm region of 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: embryonic disc, showing the epibl