Development of GIT associated organs Flashcards
Which of the abdominal organs are formed from outpocketings of the foregut? Which section of the foregut do they develop from?
Liver, gallbladder, pancreas. Develop as diverticulum of the cranial half of the duodenum.
In what week does the hepatic diverticulum develop?
Week 3
How does the hepatic diverticulum contact the diaphragm?
It contains rapidly proliferating cells that pierce the septum transversum.
From which germ layer are hepatocytes derived?
Endoderm
From which germ layer are haematopoietic, Kupffer and connective tissue cells derived?
Mesoderm of the septum transversum.
What happens when the liver begins the rapidly expand?
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.
What happens to the mesoderm on the surface of the liver?
Differentiates into visceral peritoneum except on cranial surface.
What happens to the cranial surface of the liver?
Remains in contact with the septum transversum - becomes the bare area of the liver.
What happens to the peritoneum around the margins of the bare area?
Reflects to form the coronary ligament, which also forms the L and R triangular ligaments.
What function does the liver perform in utero?
Haematopoiesis
Describe the development of the gall bladder.
Forms as an outgrowth of the bile duct to form the gallbladder and cystic duct.
In what week does the liver start to produce bile?
Week 12
How is bilrubin removed from foetal circulation prior to birth?
Crosses the placenta and removed via the mother’s circulation. After birth liver conjugates bilirubin.
What is neonatal jaundice?
In 60% of full term infants the liver does not have sufficient glucuronosyltransferase to conjugate bilirubin - hyperbilirubinaemia.
What are the potential consequences of untreated neonatal jaundice?
Kernicterus - bilirubin induced encephalopathy. Phototherapy oxidises bilirubin to a water soluble form that can be excreted. Blue light most effective.
What is biliary atresia?
Failure of the bile duct to recanalise. 1 in 15,000 births. Causes jaundice that does not respond to phototherapy.
How does duplication of the gallbladder occur?
Extra endodermal outpocketing during weeks 5 and 6.
From what does the dorsal bud of the pancreas develop?
From the duodenum as an outpocketing in week 3.
Where does the ventral bud of the pancreas appear?
As a smaller diverticulum caudal to the developing gallbladder.
How do the two buds of the pancreas come to lie next to each other?
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.
What structures develop from the dorsal bud of the pancreas?
Head, body and tail.
What structure develops from the tail of the pancreas.
Uncinate process.
From which germ layer is pancreatic connective tissue and vasculature derived?
Mesoderm
What forms the main pancreatic duct?
Distal portion of dorsal pancreatic duct and all of ventral pancreatic duct.
What forms the accessory pancreatic duct?
Proximal portion of the dorsal pancreatic duct. May become obliterated during development.
What is an annular pancreas?
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.
Where might ectopic pancreatic tissue be found?
Distal oesophagus to tip of primary intestinal loop.
What is the aetiology of ectopic pancreatic tissue?
Inappropriate differentiation of endodermal cells into pancreatic tissue.
How does the spleen differ from all other abdominal organs?
Not derived from endoderm. Derived from mesoderm.
What structure does the spleen develop from?
From the dorsal mesentery as a mesenchymal condensation.
What does the dorsal mesentery between the stomach and the spleen become?
The gastrosplenic ligament.
What does the dorsal mesentery between the spleen and the kidney become?
The splenorenal (lienorenal) ligament.
What percentage of the population have accessory spleens and where do they usually form?
10% - usually form near the hilum of the primary spleen.
