Embryology

Question 1

At what point are the gall bladder, pancreas and liver attached to the foregut?

Answer 1

Sphincter of Odd/ Major duodenal Papilla (same thing)

Question 2

The liver, gall bladder and pancreas develop as diverticulum from where?

Answer 2

The cranial half of the duodenum

Question 3

In which week does the hepatic diverticulum (liver bud) appear?

Answer 3

Week 3

Question 4

The hepatic diverticulum contains rapidly proliferating cells which penetrate what?

Answer 4

The septum transversum (future diaphragm)

Question 5

What do the connections between the hepatic diverticulum and duodenum narrow to form?

Answer 5

The bile duct

Question 6

From which germ layer are hepatocytes (liver parenchyma) derived?

Answer 6

Endoderm (gut tube is derived from endoderm)

Question 7

From which germ layer are the kupffer, haematopoietic cells and connective tissue of the liver derived from?

Answer 7

Mesoderm of the septum transversum

Question 8

What are haematopoietic cells?

Answer 8

Stem cells which make new RBC’s

Question 9

What is the relationship between the development of the liver and herniation of the midget?

Answer 9

Liver grows so rapidly that in order to have space to elongated the mid gut is forced to herniate

Question 10

What happens to the mesentery as the liver increases rapidly in size?

Answer 10

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

Question 11

How does the visceral peritoneum of the liver develop?

Answer 11

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

Question 12

What percentage of total body weight does the liver make up at week 10?

Answer 12

10%

Question 13

What percentage of total body weight does the liver make up at birth?

Answer 13

5%

Question 14

Why is the liver so large relative to the body in utero compared to birth?

Answer 14

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

Question 15

When does the gallbladder begin to develop?

Answer 15

End of week 3

Question 16

When does the liver start to produce bile?

Answer 16

Week 12

Question 17

How does the gall bladder begin to develop?

Answer 17

A central outgrowth of the bile duct forms the gall bladder and cystic duct

Question 18

What is Meconium?

Answer 18

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

Question 19

How is Bilirubin handled by the embryo in utero?

Answer 19

Bilirubin crosses the placenta and is removed by the mothers circulation

Question 20

Why does neonatal jaundice commonly occur?

Answer 20

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)

Question 21

What is kernicterus and why does it occur?

Answer 21

Complication of untreated neonatal jaundice, excess unconjugated Bilirubin crosses the BBB and causes brain damage

Question 22

How can neonatal jaundice be treated?

Answer 22

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

Question 23

What is biliary atresia and why does it occur?

Answer 23

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

Question 24

How many births are affected by biliary atresia?

Answer 24

1 in 15,000 births

Question 25

What is duplication of the gall bladder and does it have any symptoms?

Answer 25

Common congenital malformation, usually asymptomatic, caused by an extra endodermal outpocketing during week 5 or 6, triple gall bladders have also been reported

Question 26

When does the pancreas begin to develop?

Answer 26

Week 3

Question 27

How does the pancreas develop initially?

Answer 27

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

Question 28

How do the ventral bud and the dorsal bud of the pancreas fuse?

Answer 28

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

Question 29

At what week in development do the ventral and dorsal buds of the pancreas fuse?

Answer 29

Week 6

Question 30

After the stomach has rotated where does the dorsal bud lie in relation to the ventral bud?

Answer 30

Ventral bud lies posterior to the dorsal bud

Question 31

What part of the pancreas does the dorsal bud give rise to?

Answer 31

Head, body and tail

Question 32

What part of the pancreas does the ventral bud give rise to?

Answer 32

Uncinate process

Question 33

What forms the connective tissue and blood vessels of the pancreas?

Answer 33

The surrounding mesoderm

Question 34

What is the main pancreatic duct formed from?

Answer 34

Distal portion of the dorsal pancreatic duct and ALL of the ventral pancreatic duct

Question 35

What is the accessory pancreatic duct formed from?

Answer 35

Proximal portion of the dorsal pancreatic duct however accessory pancreatic duct may be obliterated during development

Question 36

Where does the main pancreatic duct enter the duodenum?

Answer 36

At the major duodenal papilla (ampulla of vater) as does the bile duct

Question 37

Where does the accessory pancreatic duct enter the duodenum?

Answer 37

At the minor duodenal papilla (cranial to the major one)

Question 38

What is an annular pancreas and does it have any symptoms?

Answer 38

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

Question 39

What is an annular pancreas and does it have any symptoms?

Answer 39

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

Question 40

What is ectopic pancreatic tissue?

Answer 40

Inappropriate differentiation of endodermal cells into pancreatic tissue

Question 41

Where does ectopic pancreatic tissue most commonly occur?

Answer 41

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

Question 42

Which germ layer does the spleen arise from?

Answer 42

The mesoderm

Question 43

In which week of development does the spleen begin to develop?

Answer 43

Week 5

Question 44

How does the spleen develop?

Answer 44

As a mesenchymal condensation in the dorsal mesentery (mesoderm condences to from mesenchyme which differentiates to become the spleen)

Question 45

How does the spleen come to be on the left hand side?

Answer 45

The rotation of the stomach bring the spleen over to the left hand side

Question 46

What happens to the dorsal mesentery as the spleen develops?

Answer 46

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

Question 47

Why might an accessory spleen develop?

Answer 47

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

Question 48

Why is an accessory spleen an important variation to be aware of?

Answer 48

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