Lecture Tuesday September 4: GI Embryology III

The spleen is NOT a derivative of the GI tract!

Liver Development
Liver grows from the primitive gut tube into the ventral mesentery/septum transversum which becomes the lesser omentum and falciform ligament.

Cranial portion of ventral mesentery/septum transversum contributes to the formation of the diaphragm (central tendon). Muscle of diaphragm from somitic mesoderm (epimeres).

Vitelline veins form hepatic sinusoids, hepatic veins and ductus venosus.

Pancreas Development
- Dorsal pancreatic bud: part of the head, all of body and tail. Accessory pancreatic duct
- Ventral pancreatic bud: outgrowth from the main bile duct. "rotates posteriorly" uncinate process and part of the head. Main pancreatic duct.

Clinical condition:
1. Annular/ring Pancreas (overgrowth of ventral pancreatic bud)

Midgut Development
- The midgut loop extends into the umbilical cord at 6 weeks of development
- The midgut loop rotates and returns to the abdominal cavity at 10 weeks of development producing the normal pattern seen in the adult.

Clinical conditions:
1. Malrotation: positions the whole of the small intestine on right and large intestine on left or puts the duodenum anterior to the transverse colon which may obstruct the duodenum.








2. Failure of recanalization of the gut tube: abnormal lumen partially or completely blocked (stenosis). Imperforate anus (no anal opening)

3. omphalocele: failure of the midgut to return to the abdominal cavity. Portion of gut surrounded by peritoneum within the umbilical cord.

4. Gastroschisis: herniation of gut outside of abdominal wall. Failure of abdominal wall to form correctly. Herniated gut Not covered by peritoneal sac or umbilical cord.

5. Meckel's diverticulum: persistent yolk stalk off of the ilium.



6. Hirschsprung's disease (aganglionic mega colon)
Failure of neural crest to migrate into distal colon to form ganglia of the Myenteric and submucosal plexus. The affected segment of the colon fails to relax causing an obstruction and proximal dilation.



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