Development of GIT associated organs

Question 1

Which of the abdominal organs are formed from outpocketings of the foregut? Which section of the foregut do they develop from?

Answer 1

Liver, gallbladder, pancreas. Develop as diverticulum of the cranial half of the duodenum.

Question 2

In what week does the hepatic diverticulum develop?

Answer 2

Week 3

Question 3

How does the hepatic diverticulum contact the diaphragm?

Answer 3

It contains rapidly proliferating cells that pierce the septum transversum.

Question 4

From which germ layer are hepatocytes derived?

Answer 4

Endoderm

Question 5

From which germ layer are haematopoietic, Kupffer and connective tissue cells derived?

Answer 5

Mesoderm of the septum transversum.

Question 6

What happens when the liver begins the rapidly expand?

Answer 6

Becomes too large to be contained within the septum transversum - protrudes into ventral mesentery, dividing the mesentery into two parts - falciform ligament and lesser omentum.

Question 7

What happens to the mesoderm on the surface of the liver?

Answer 7

Differentiates into visceral peritoneum except on cranial surface.

Question 8

What happens to the cranial surface of the liver?

Answer 8

Remains in contact with the septum transversum - becomes the bare area of the liver.

Question 9

What happens to the peritoneum around the margins of the bare area?

Answer 9

Reflects to form the coronary ligament, which also forms the L and R triangular ligaments.

Question 10

What function does the liver perform in utero?

Answer 10

Haematopoiesis

Question 11

Describe the development of the gall bladder.

Answer 11

Forms as an outgrowth of the bile duct to form the gallbladder and cystic duct.

Question 12

In what week does the liver start to produce bile?

Answer 12

Week 12

Question 13

How is bilrubin removed from foetal circulation prior to birth?

Answer 13

Crosses the placenta and removed via the mother’s circulation. After birth liver conjugates bilirubin.

Question 14

What is neonatal jaundice?

Answer 14

In 60% of full term infants the liver does not have sufficient glucuronosyltransferase to conjugate bilirubin - hyperbilirubinaemia.

Question 15

What are the potential consequences of untreated neonatal jaundice?

Answer 15

Kernicterus - bilirubin induced encephalopathy. Phototherapy oxidises bilirubin to a water soluble form that can be excreted. Blue light most effective.

Question 16

What is biliary atresia?

Answer 16

Failure of the bile duct to recanalise. 1 in 15,000 births. Causes jaundice that does not respond to phototherapy.

Question 17

How does duplication of the gallbladder occur?

Answer 17

Extra endodermal outpocketing during weeks 5 and 6.

Question 18

From what does the dorsal bud of the pancreas develop?

Answer 18

From the duodenum as an outpocketing in week 3.

Question 19

Where does the ventral bud of the pancreas appear?

Answer 19

As a smaller diverticulum caudal to the developing gallbladder.

Question 20

How do the two buds of the pancreas come to lie next to each other?

Answer 20

The ventral bud is carried dorsally along with the bile duct as the duodenum rotates 90 degrees. The ventral pancreatic bud comes to lie posterior to dorsal bud.

Question 21

What structures develop from the dorsal bud of the pancreas?

Answer 21

Head, body and tail.

Question 22

What structure develops from the tail of the pancreas.

Answer 22

Uncinate process.

Question 23

From which germ layer is pancreatic connective tissue and vasculature derived?

Answer 23

Mesoderm

Question 24

What forms the main pancreatic duct?

Answer 24

Distal portion of dorsal pancreatic duct and all of ventral pancreatic duct.

Question 25

What forms the accessory pancreatic duct?

Answer 25

Proximal portion of the dorsal pancreatic duct. May become obliterated during development.

Question 26

What is an annular pancreas?

Answer 26

The ventral pancreatic bud can be bilobed. One lobe miy migrate dorsally and the other ventrally to surround the duodenum. This can cause GI obstruction.

Question 27

Where might ectopic pancreatic tissue be found?

Answer 27

Distal oesophagus to tip of primary intestinal loop.

Question 28

What is the aetiology of ectopic pancreatic tissue?

Answer 28

Inappropriate differentiation of endodermal cells into pancreatic tissue.

Question 29

How does the spleen differ from all other abdominal organs?

Answer 29

Not derived from endoderm. Derived from mesoderm.

Question 30

What structure does the spleen develop from?

Answer 30

From the dorsal mesentery as a mesenchymal condensation.

Question 31

What does the dorsal mesentery between the stomach and the spleen become?

Answer 31

The gastrosplenic ligament.

Question 32

What does the dorsal mesentery between the spleen and the kidney become?

Answer 32

The splenorenal (lienorenal) ligament.

Question 33

What percentage of the population have accessory spleens and where do they usually form?

Answer 33

10% - usually form near the hilum of the primary spleen.