Embryology Flashcards
At what point are the gall bladder, pancreas and liver attached to the foregut?
Sphincter of Odd/ Major duodenal Papilla (same thing)
The liver, gall bladder and pancreas develop as diverticulum from where?
The cranial half of the duodenum
In which week does the hepatic diverticulum (liver bud) appear?
Week 3
The hepatic diverticulum contains rapidly proliferating cells which penetrate what?
The septum transversum (future diaphragm)
What do the connections between the hepatic diverticulum and duodenum narrow to form?
The bile duct
From which germ layer are hepatocytes (liver parenchyma) derived?
Endoderm (gut tube is derived from endoderm)
From which germ layer are the kupffer, haematopoietic cells and connective tissue of the liver derived from?
Mesoderm of the septum transversum
What are haematopoietic cells?
Stem cells which make new RBC’s
What is the relationship between the development of the liver and herniation of the midget?
Liver grows so rapidly that in order to have space to elongated the mid gut is forced to herniate
What happens to the mesentery as the liver increases rapidly in size?
Liver becomes too large to be contained within the septum transversum, liver descends below the diaphragm and protrudes into the ventral mesentery, this divides the ventral mesentery into 2 parts:
1) The falciform ligament
2) The lesser omentum
How does the visceral peritoneum of the liver develop?
Mesoderm on the surface differentiates into visceral peritoneum except on the cranial surface which remains in contact with the diaphragm and becomes the bare area of the liver, peritoneum reflects to form the coronary ligament which ultimately ends at the lateral edges of the liver forming the triangular ligament
What percentage of total body weight does the liver make up at week 10?
10%
What percentage of total body weight does the liver make up at birth?
5%
Why is the liver so large relative to the body in utero compared to birth?
In utero the liver carries out haematopoietic, at birth this role is shifted to the bone marrow as the bone marrow cells are now sufficiently matured and the liver decreases in size
When does the gallbladder begin to develop?
End of week 3
When does the liver start to produce bile?
Week 12
How does the gall bladder begin to develop?
A central outgrowth of the bile duct forms the gall bladder and cystic duct
What is Meconium?
First bowel movement of the new born, its dark green in colour as it contains the bile released into the GI tract by the liver in utero - good sign as it means the liver is functioning and there is no obstruction in the GI tract
How is Bilirubin handled by the embryo in utero?
Bilirubin crosses the placenta and is removed by the mothers circulation
Why does neonatal jaundice commonly occur?
In 60% full term infants the immature liver does not have sufficient glucuronosyltransferase to conjugate Bilirubin so it can be excreted - get hyperbilrubinaemia (jaundice), get yellow skin and sclera (whites of the eyes)
What is kernicterus and why does it occur?
Complication of untreated neonatal jaundice, excess unconjugated Bilirubin crosses the BBB and causes brain damage
How can neonatal jaundice be treated?
Phototherapy oxidises the Bilirubin to a water soluble form which can be easily excreted by the new born and does not contribute to kernicterus - blue light is the most effective
What is biliary atresia and why does it occur?
Like the GI tract, the hepatic duct and bile duct epithelium undergo proliferation and recanalization (important for cell differentiation), biliary atresia occurs when either the bile duct or hepatic duct fail to recanalize - excretion of bile (and therefore conjugated Bilirubin) is blocked, causes symptoms that are initially indistinguishable from neonatal jaundice but can’t be treated with phototherapy, however don’t contribute to kernicterus as conjugated Bilirubin can’t cross the BBB
How many births are affected by biliary atresia?
1 in 15,000 births
What is duplication of the gall bladder and does it have any symptoms?
Common congenital malformation, usually asymptomatic, caused by an extra endodermal outpocketing during week 5 or 6, triple gall bladders have also been reported
When does the pancreas begin to develop?
Week 3
How does the pancreas develop initially?
As 2 endodermal buds that fuse together, dorsal bud develops as an outpocketing of the duodenum that extends into the dorsal mesentery and the ventral bud appears as a smaller diverticulum caudal to the gall bladder
How do the ventral bud and the dorsal bud of the pancreas fuse?
As the duodenum rotates 90 degrees clockwise, as the stomach rotates the ventral bud is carried dorsally along with the bile duct and the ventral buds and dorsal buds fuse
At what week in development do the ventral and dorsal buds of the pancreas fuse?
Week 6
After the stomach has rotated where does the dorsal bud lie in relation to the ventral bud?
Ventral bud lies posterior to the dorsal bud
What part of the pancreas does the dorsal bud give rise to?
Head, body and tail
What part of the pancreas does the ventral bud give rise to?
Uncinate process
What forms the connective tissue and blood vessels of the pancreas?
The surrounding mesoderm
What is the main pancreatic duct formed from?
Distal portion of the dorsal pancreatic duct and ALL of the ventral pancreatic duct
What is the accessory pancreatic duct formed from?
Proximal portion of the dorsal pancreatic duct however accessory pancreatic duct may be obliterated during development
Where does the main pancreatic duct enter the duodenum?
At the major duodenal papilla (ampulla of vater) as does the bile duct
Where does the accessory pancreatic duct enter the duodenum?
At the minor duodenal papilla (cranial to the major one)
What is an annular pancreas and does it have any symptoms?
Ventral pancreatic bud can be bi lobed, in this case one part may migrate ventrally and one part migrate dorsally to the duodenum (should migrate dorsally) and fuse with the dorsal pancreatic bud so you end up with a pancreas surrounding the duodenum- annular pancreas. Can be asymptomatic but can compress the duodenum causing GI obstruction - green colour missing from meconium in first bowel movement
What is an annular pancreas and does it have any symptoms?
Ventral pancreatic bud can be bi lobed, in this case one part may migrate ventrally and one part migrate dorsally to the duodenum (should migrate dorsally) and fuse with the dorsal pancreatic bud so you end up with a pancreas surrounding the duodenum- annular pancreas. Can be asymptomatic but can compress the duodenum causing GI obstruction - green colour missing from meconium in first bowel movement
What is ectopic pancreatic tissue?
Inappropriate differentiation of endodermal cells into pancreatic tissue
Where does ectopic pancreatic tissue most commonly occur?
Can be found in areas ranging from the distal oesophagus to the tip of the primary intestinal loop, most frequently in duodenum or stomach muscosa. Usually asymtomatic but can occur in tissues such as the lung or spleen and can end up with auto digestion - large lesions can cause obstruction, ulceration or hemorrhage
Which germ layer does the spleen arise from?
The mesoderm
In which week of development does the spleen begin to develop?
Week 5
How does the spleen develop?
As a mesenchymal condensation in the dorsal mesentery (mesoderm condences to from mesenchyme which differentiates to become the spleen)
How does the spleen come to be on the left hand side?
The rotation of the stomach bring the spleen over to the left hand side
What happens to the dorsal mesentery as the spleen develops?
Becomes 2 different bits:
1) The dorsal mesentery between the spleen and the stomach = the gastrosplenic ligament
2) The dorsal mesentery between the spleen and the left kidney = the lienorenal (splenorenal) ligament
Why might an accessory spleen develop?
Additional condensations may occur in the dorsal mesentery and form and accessory spleen - occurs in 10% of the population - they normally develop near the hilum of the spleen
Why is an accessory spleen an important variation to be aware of?
Usually asymptomatic but can affect interpretation of medical images and is important for surgeons to be aware of, as spleen has a very rich blood supply and rupture of an accessory spleen could lead to a massive bleed
