File:Stage7 lateral-plate.jpg

Lateral plate mesoderm lies outside the intermediate mesoderm and extending around the edge of the embryonic disc.

The lateral plate mesoderm is split by a cavity, the intraembryonic coelom, forming two separate components:

1. Somatic mesoderm - underlying the ectoderm
2. Splanchnic mesoderm - underlying the endoderm

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.

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.

• Blue dot (top) - buccopharyngeal membrane
• Blue dot (middle) - primitive node
• Blue dot (bottom) - cloacal membrane
• Orange line - axial mesoderm (future notochord)
• Orange bands (inner) - paraxial mesoderm, lateral to axial mesoderm (future somites and unsegmented mesoderm in head region)
• Orange bands (middle) - intermediate mesoderm (future urogenital structures, renal and internal genital)
• Orange region (outer) - lateral plate mesoderm (future somatic and splanchnic mesoderm and intraembryonic coeloms)
• grey line - primitive streak

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

Stage 7 Mesoderm: axial | paraxial | intermediate | lateral plate