Development of the GI Tract

Question 1

What forms the gut epithelium and mesenteries?

Answer 1

• Pinched off endoderm - forms primary gut epithelia

* Surrounding somatic and splanchnic mesoderm - forms the mesentery

Question 2

How is the gut tube formed?

Answer 2

• Embryo initially a solid, flat disk attached to the yolk sac
• Part of the yolk sac cavity is enclosed within the embryo by pinching-off the yolk sac to form a yolk stalk and balloon-like yolk sac
• Within embryo, cranial and caudal intestinal portals extend the tube towards the mouth and anus

Question 3

What are the regions of the gut?

What defines the regions?

Where do the sympathetic ganglia form? What do they innervate?

Answer 3

• Foregut, Midgut, Hindgut
• Their blood supply - Foregut supplied by Coeliac trunk, Midgut by SMA, Hindgut by IMA.
• Next to the major branches of the abdominal aorta. They innervate the same places their corresponding artery supplies.

Question 4

What movements form the stomach?

How is the stomach formed?

Describe the mesentery attachments

LOOK AT PICTURES!

Answer 4

• Rotation, Expansion
• It rotates 90 degrees around the axis with the pylorus moving cranially. Surfaces then begin to concave and convex.
• The dorsal stomach is attached to body wall by the Dorsal MESOGASTRIUM, and the ventral by the Ventral MESOGASTRIUM. In the middle of the ventral mesogastrium is the Liver, which then divides the mesogastrium into the Lesser omentum and Falciform ligament.

Question 5

What forms from the budding of the liver? Where does it bud off?

What do the dorsal and ventral pancreatic buds form? How?

Answer 5

• It buds off near the heart and differentiates into the bile ducts, blood vessels, and sinusoids.
• The pancreas - as duodenum rotates, the buds meet and fuse to form the whole pancreas.

Question 6

How do the intestines form?

What gives rise to the rectum?

Answer 6

• The intestines rapidly increase in length and they rotate around the SMA. But the abdomen is too small to accommodate all of it, so it herniates into the umbilical stalk. After a few weeks, the abdomen will have grown enough to accommodate the intestines.
• Cloaca