Development of Gastrointestinal Associated Organs Flashcards
What is the epithelial lining of the gut tube derived from?
How does this affect the development of GIT-associated organs?
The epithelial lining is derived from endoderm
Other than the spleen, most GIT-associated organs are derived from endoderm
How are the liver, gallbladder and pancreas formed?
They are outpocketings of endoderm in the cranial half of the duodenum
What is duodenal papilla?
It delineates the change between the embryological foregut and midgut
It is the region where secretions from the accessory organs are emptied into the 2nd half of the duodenum
During which week does the liver begin to develop?
How does it first appear?
week 3
it appears as an outpouching of endoderm from the foregut
This is the hepatic diverticulum (liver bud)
What is the liver bud often called?
An endodermal plate
It is thickening of the endoderm at the cranial end of the duodenum
What happens to the rapidly dividing cells in the hepatic diverticulum?
They penetrate the septum transversum
this goes on to form the diaphragm
Why does the liver contain some cells of mesodermal origin?
The septum transversum is of mesodermal origin
Some of the mesodermal cells become encompassed within the liver
What is formed from the connections between the hepatic diverticulum and the duodenum?
The bile duct
What will endodermal cells develop into in the liver?
Endodermal cells develop into hepatocytes (parenchyma) of the liver
What will be derived from the mesoderm of the septum transversum?
Haematopoietic cells
Kupffer cells
connective tissue
What is the primary function of the liver in the developing foetus?
Why is this different in an adult?
Haematopoiesis - making blood cells
The liver of a foetus does not need to process metabolites from digestion as the mother does this
Why does the function of the liver change after birth?
The baby must process the nutrients from the GI tract and make them usable
What happens to haematopoiesis after birth?
It shifts to the bone marrow instead
Why does the midgut herniate into the Vitelline duct?
The liver continues to rapidly expand, as does the small intestine
There is not enough space for both of them
What happens when the liver can no longer be contained within the septum transversum?
It protrudes into the ventral mesentery and divides it into 2 parts:
- falciform ligament
- lesser omentum
Where do the falciform ligament and lesser omentum run to and from?
The lesser omentum runs from the stomach to the liver
The falciform ligament runs from the liver to the ventral wall
They are both derivatives of the ventral mesentery
As the liver grows caudally, what is it in contact with?
What does this lead to?
The cranial part of the liver is in contact with the septum transversum
As they are so closely related, the bare area of the liver does not have any peritoneal covering on it
What happens to the mesoderm on the surface of the liver?
It differentiates into the visceral peritoneum, except on the cranial surface
What happens to the cranial surface of the liver during differentiation of the mesoderm?
It becomes the bare area of the liver as it remains in contact with the septum transversum
What forms around the margins of the bare area?
What are they formed from?
The peritoneum reflects to form anterior and posterior coronary ligaments
These are formed from mesoderm
What are the triangular ligaments formed from?
Where the anterior and posterior coronary ligaments meet at the lateral edges of the liver
What is the % of body weight taken up by the liver during week 10 of development?
How does this change after birth?
At week 10, the liver is 10% of total body weight
This decreases to 5% after birth
When does the gallbladder form?
What does it form from?
Forms at the end of week 3
a ventral outgrowth of the bile duct forms the gallbladder and cystic duct
this is an endodermal thickening
When does the foetus start producing bile?
What happens to it?
The liver starts producing bile in week 12
This is released into the GI tract but it has nowhere to go until the baby is born
What is the meconium?
The first bowel movement of the newborn
What colour is the meconium and why?
It is dark green in colour
This is due to the high concentration of bile
What happens to bilirubin prior to birth?
Bilirubin crosses the placenta and is removed by the mother’s circulation
What happens to bilirubin after birth?
Why is this necessary?
The liver conjugates bilirubin
This makes it water-soluble
It can then be excreted into the GI tract through the biliary system
What is the enzyme needed to conjugate bilirubin?
Glucuronosyltransferase
What happens if the immature liver does not contain enough glucuronosyltransferase?
Bilirubin cannot be sufficiently conjugated and secreted
It accumulates - hyperbilirubinaemia
This leads to neonatal jaundice
What are the characteristic signs of neonatal jaundice?
Yellow skin and sclera
What is the main complication of neonatal jaundice if it is untreated?
If the bilirubin builds up in the blood supply, it can cross the blood-brain barrier and cause problems with development of the brain
This is kernicterus
How is neonatal jaundice treated?
Phototherapy (light therapy)
Blue light is the most effective
How can phototherapy prevent the risks of kernicterus?
Phototherapy oxidises bilirubin to a water-soluble form that can be easily excreted
What causes biliary atresia?
Failure of the hepatic or bile duct to recanalise
What happens during recanalisation of the hepatic and bile ducts?
Cells in the tube proliferate quickly to fill the tube and make it a solid structure
Apoptosis then forms small holes in the tube
These holes join together to make a hollow lumen
how many births are affected by biliary atresia?
1 in 15,000
What is biliary atresia and what does it lead to?
The bile duct is narrowed, leading to a distended hepatic duct
Why is biliary atresia often initially treated with phototherapy?
It presents with symptoms which are indistinguishable from neonatal jaundice
How can biliary atresia be distinguished from neonatal jaundice?
As soon as phototherapy stops, the symptoms of jaundice will return
What causes duplication of the gallbladder?
An extra endodermal outpocketing during weeks 5 and 6
This leads to formation of 2 gallbladders
What are the symptoms of duplication of the gallbladder?
It is usually asymptomatic
What does the pancreas initially develop as?
2 endodermal buds which fuse together
These are the dorsal and ventral buds
Which pancreatic endodermal bud develops first?
How does it develop?
The dorsal bud appears in week 3
It is an outpocketing of the duodenum that extends into the dorsal mesentery
Where does the ventral bud develop?
The ventral bud is a smaller diverticulum that is caudal to the developing gallbladder
What happens as the stomach and duodenum rotate 90o to the endodermal buds?
The ventral bud is carried dorsally along with the bile duct
It will fuse with the inferior edge of the dorsal bud during week 6
What do the dorsal and ventral buds give rise to?
The dorsal bud gives rise to the head, body and tail of the pancreas
The ventral bud gives rise to the uncinate process
What are the connective tissue and blood vessels surrounding the pancreas formed from?
Mesoderm
What happens to the ductal systems when the dorsal and ventral buds fuse?
Their ductal systems become interconnected
What is the main pancreatic duct formed from?
The distal portion of the dorsal pancreatic duct and ALL of the ventral pancreatic duct
what is the accessory pancreatic duct formed from?
What is significant about this?
Formed from the proximal portion of the dorsal pancreatic duct
It is often obliterated during development
Where does the main pancreatic duct enter the duodenum?
The main pancreatic duct and bile duct enter the duodenum at the Ampulla of Vater
This is the major duodenal papilla
How is the Ampulla of Vater controlled?
Contraction and relaxation of the sphincter of Oddi to allow secretions into the second part of the duodenum
Where would the accessory pancreatic duct enter the duodenum?
at the minor duodenal papilla
What condition results from a bilobed ventral pancreatic duct?
How does this happen?
One lobe may migrate ventral to the duodenum and one love may migrate dorsally to surround the duodenum
This leads to annular pancreas
What is the consequence of annular pancreas?
It compresses the duodenum and causes gastrointestinal obstruction
What is meant by ectopic pancreatic tissue?
Inappropriate differentiation of endodermal cells into pancreatic tissue
This leads to pancreatic tissue being in places where it shouldn’t
Where is ectopic pancreatic tissue found?
Anywhere from the distal oesophagus to the tip of the primary intestinal loop
It is most frequently in the duodenum or stomach muscosa
What are the symptoms of ectopic pancreatic tissue?
It is usually asymptomatic
If the tissue begins to secrete enzymes, it begins to degrade the gut tube wall
This leads to ulceration or haemorrhage
When does the spleen first appear?
From what is it derived?
It appears in week 5
It is a mesenchymal condensation in the dorsal mesentery
It is derived from mesoderm
What is mesenchyme?
Undifferentiated mesoderm
How does rotation of the stomach affect the spleen?
Rotation of the stomach brings the spleen over to the left-hand sidee
How does the spleen divide the dorsal mesentery?
The gastrosplenic ligament is between the stomach and the spleen
The lienorenal (splenorenal) ligament is between the spleen and kidney
What causes an accessory spleen?
How common are they?
Additional mesenchymal condensations may occur in the dorsal mesentery
10% of the population have an accessory spleen
Where do accessory spleens usually form?
Near the hilum of the primary spleen
What are they symptoms of an accessory spleen?
Why is it important to recognise?
Usually asymptomatic
It can affect the interpretation of medical images
