Alimentary - development of the GIT

Question 1

What is the gut produced from?

Answer 1

Endoderm

Question 2

How does the endoderm form the gut?

Answer 2

1. The endorderm folds and elevates. This becomes the splanchnic mesoderm.
2. The endoderm folds around ventrally and fuses
3. The endoderm turns into a sheet of epithelial cells adjacent to the lumen. The splanchinic mesoderm forms the connective tissues, smooth muscle and mesothelial layers
4. Eventually this tube of endoderm layered with splanchnic mesoderm joins to yolk sac extra embryonic mesoderm. This forms the mesenteric

Question 3

What is the primtive gut tube?

Answer 3

Foregut, midgut and hindgut, a continuous tube.

The “mouth”/anterior end meets ectoderm of oral cavity at buccopharyngeal membrane

The “anus”/posterior end meets endoderm at cloacal membrane.

Question 4

What happens in these membranes are not perforated?

Answer 4

There can be sealed mouths/anus which is common in sheep.

Question 5

What consists of the foregut?

Answer 5

Oesophagus
Liver
Stomach
Gallbladder
Bile ducts
Pancreas
Proximal duodenum

Question 6

How does the foregut form?

Answer 6

1. The tube turns 90 degrees clockwise on the long axis
2. Bulges out the left
3. Turns, tilting down and to the left forming the greater and lesser curvature

Question 7

What does the dorsal mesentery give rise to?

Answer 7

To the greater omentum, attaching the greater curve of the stomach to the dorsal wall

This contains the gastrophrenic, gastrocolic and gastrosplenic ligaments.

This forms the spleen.

Question 8

What does the ventral mesentery give rise to?

Answer 8

The lesser omentum, which attaches the lesser curvator to the ventral abdominal wall.

This contains the hepatophrenic and hepatooesophageal ligaments, and falciform ligaments.

This forms the liver.

Question 9

What artery supplies the foregut?

Answer 9

Coelic branch of aorta

Question 10

What creates the liver, pancreas and gall bladder?

Answer 10

The budding of the duodenal endoderm.

Spleen in ventral mesentry
Liver in dorsal mesentry

Pancreas forms on either side, and as the duodenum rotates the two ducts meet forming the pancreas with minor and major ducts.

Question 11

What does the midgut consist of?

Answer 11

Distal half of the duodenum, jejunum, ileum, caecum, ascending colon and proximal half of trasnverse colon.

Question 12

What circulation supplies the midgut?

Answer 12

Cranial mesenteric branch of aorta

Question 13

How is the midgut formed?

Answer 13

1. The tube is pushed out of the vitelline duct as the foregut grows
2. It rotates 90 degrees around cranial mesenteric artery, and tube on the cranial forms the caecum and the proximal part forms the jejunolieal loops.
3. As the abdomen grows the midgut sucks back in. Proximal joins first, rotating as it does to move to left hand side and distal portion re-enters to right hand side.

Question 14

What forms the hindgut?

Answer 14

Rest of the large intestine

Question 15

What circulation supplies the hindgut?

Answer 15

Caudal mesenteric branch of aorta

Question 16

Whats the urogenital tract?

Answer 16

Part of the hindgut which eventually splits