TBL18 - Differentiation of the Liver, Gallbladder and Pancreas

Question 1

Where is the liver bud specifically derived from? What does this portion of the small intestine represent?

Answer 1

1) The liver bud is an endodermal outgrowth from the 2nd part of the duodenum
2) The site of endodermal outgrowth marks the end of the foregut-derived portion of the duodenum

Question 2

What does the initial outgrowth of the liver bud form? What is a ventral outgrowth from the bile duct? How is the gallbladder formed?

Answer 2

1) The initial outgrowth of the liver bud forms the bile duct
2) A ventral outgrowth from the bile duct forms the cystic duct
3) The gallbladder is formed by proliferation of the cystic duct epithelium within the septum transversum

Question 3

What does the bile duct divide into distal to the cystic duct? What are the liver cords formed from? Where do the liver cords proliferate into?

Answer 3

1) Distal to the cystic duct, the bile duct divides into the right and left hepatic ducts
2) The liver cords are formed by epithelial proliferation from the hepatic ducts
3) The liver cords proliferate into the septum transversum

Question 4

What do the liver cords differentiate into? What makes up the liver stroma? What makes up the hepatic sinusoids and hepatic veins?

Answer 4

1) With further development, the liver cords differentiate into hepatocytes (parenchymal liver cells)
2) Mesenchymal cell-derived fibroblasts in the septum transversum generate the liver stroma
3) The right and left vitelline veins form the hepatic sinusoids and hepatic veins

Question 5

Aside from the liver buds, what other endodermal outgrowths form from the 2nd part of the duodenum? Where are the dorsal and ventral portions located?

Answer 5

1) Adjacent to the bile duct, endodermal outgrowths from the 2nd part of the duodenum form dorsal and ventral pancreatic buds
2) The large dorsal pancreatic bud grows into the dorsal mesentery and the small ventral bud remains close to the proximal portion of the bile duct

Question 6

What occurs to the duodenum during the stomach’s rotation around its anteroposterior axis? What happens to the ventral and dorsal pancreatic buds during this rotation? Where do the conjoined buds lie after the rotation of the stomach?

Answer 6

1) During the stomach’s rotation around its anteroposterior axis, the duodenum becomes C-shaped
2) During the rotation, the ventral pancreatic bud moves dorsally to join the dorsal pancreatic bud in the dorsal mesentery
3) The rotations of the stomach place the conjoined buds in the retroperitoneal space

Question 7

How is an annular pancreas formed, when can it induce vomiting that contains bile, and what creates its characteristic “double bubble” radiographic sign?

Answer 7

1) The ventral pancreatic bud consists of two components that normally fuse and rotate around the duodenum so that they come to lie below the dorsal pancreatic bud. Ocassionally, however, the right portion of the ventral bud migrates along its normal route, but the left migrates in the opposite direction. In this manner, the duodenum is surrounded by pancreatic tissue, and an annular pancreas is formed
2) The bile duct is still able to empty into the duodenum, but the annular pancreas prevents the movement of contents and bile down the duodenum. It therefore backs up to the pyloric sphincter and eventually into the stomach where vomiting will be induced
3) The double bubble radiographic sign is formed by the distended stomach and proximal duodenum

Question 8

What is a result of union of the pancreatic buds? Where does the main pancreatic duct now empty into? What is the pancreatic stroma derived from?

Answer 8

1) After union of the pancreatic buds, the endoderm-derived duct systems of the buds fuse to form the main pancreatic duct
2) The main pancreatic duct empties into the bile duct
3) The pancreatic stroma is derived from mesenchymal cells of the dorsal mesentery