BGDB Gastrointestinal - Late Embryo

Week 8

We have now reached late embryonic development. Start by looking briefly the process of how the definitive GIT tube is formed and then at the overview of the Carnegie stage 22 embryo GIT from one end to the other.

Then work through the listed specific serial sections of the embryo identifying the GIT features. Alternatively step through the serial sections yourself identifying the tract, its associated mesentries, organs and spaces. Note you should also be comparing the GIT appearance with the earlier embryonic (13/14) Carnegie stage.

Observe: GIT tube has a different appearance at different levels; stomach, duodenum, midgut and hindgut midgut herniated at the umbilicus, lying outside the ventral body wall, connected by mesentry large liver lying directly under the diaphragm and occupying the entire ventral body cavity with organs "embedded" within it the developing pancreas lying in the loop between stomach and duodenum

Lumen Development

Beginning at week 5 endoderm in the GIT wall proliferates to the extent of totally blocking (occluding) by week 6, over the next two weeks this tissue degenerates reforming a hollow gut tube. The process is called recanalization (hollow, then solid, then hollow again), abnormalities in this process can lead to duplications or stenosis.

By the end of week 8 the GIT endoderm tube is a tube once more.

In week 9 (early fetal) the endoderm of this now hollow tube differentiates into the mucosal epithelium (endoderm).

Splanchnic mesoderm will form the submucosa connective tissue and smooth muscle (circular and longitudinal) layers (mesoderm).

Neural crest cells migrate into this tissue and will form the nerve plexus innervation (ectoderm).

Glossary Links

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Cite this page: Hill, M.A. (2024, April 27) Embryology BGDB Gastrointestinal - Late Embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Gastrointestinal_-_Late_Embryo

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