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

	Gastrointestinal
Human Embryo (Carnegie stage 22, week 8	A 3D reconstruction of the gastrointestinal tract of this embryo stage.

Stage 22 Embryo - Gastrointestinal Tract

Section	Name	Description
	E6L	Liver. Ductus venosus. Cardio-oesophageal junction (cf. E5). Inferior vena cava.
	E7L	Stomach body, with mucosa, submucosa and muscularis externa. Lesser sac. Lesser omentum. Pyloroduodenal junction. Folded duodenal mucosa. Inferior vena cava. Portal vein. Hepatic ducts. Gallbladder.
	F1L	Stomach body. Spleen. Pyloric canal. Duodenum. Pancreas. Small intestine loop (jejunum) cut tangentially, ventral to liver. Portal vein.
	F2L F3L	Stomach, spleen. Superior mesenteric artery. Superior mesenteric vein crossing cranial to body of pancreas. Tail of pancreas. Duodenum. Small intestinal loop herniating from abdominal cavity into the coelom of the umbilical cord (remnant of extra-embryonic coelom).
	F4L	Greater curvature of stomach (tangential section). Lesser sac. Greater omentum. Duodenal/jejunal junction. Note colon (small lumen, darkly-staining wall) and its mesocolon. Note the sections of small and large intestine within the umbilical cord coelom and their mesenteries. Note the thickened jelly to one side of the umbilical cord, containing umbilical vein and R umbilical artery.
	F5L	Lesser sac. Greater omentum. Duodenum. Jejunum (cut twice with mesentery in between). Colon and mesocolon.
	F6L	Greater omentum and lesser sac. Jejunum with mesentery. Colon with mesocolon. Three layers of abdominal muscles. Both umbilical arteries now inside abdominal cavity with urachus between them.
	F7L	In abdominal cavity - colon with mesocolon, jejunum. Greater omentum and lesser sac. Umbilical cord - containing umbilical arteries and small dark allantois. Umbilical cord coelom containing mainly, small intestinal loops with their mesentery.
	G1L G2L	Umbilical cord and coelom containing small intestine loops. Colon and mesocolon. Jejunum (G1 only). Bladder with umbilical arteries either side. Knees.
	G3L	Rectum. Bladder. Umbilical arteries arising from common iliac arteries.
	G4L	Rectum.
	G5L	Recto-anal junction with rectovesical pouch of peritoneal cavity.
	G6L G7L	Anal canal with triangular lumen.

Lumen Development

width=252px|height=460px|controller=true|autoplay=false</qt> Quicktime | Flash

This is a simplified animation showing how the gastrointestinal tract wall changes during the late embryonic period. Week 5 - in this week 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. Week 8 - By the end of this week the GIT endoderm tube is a tube once more. 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).

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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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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G