Development of Gastrointestinal Associated Organs

Question 1

What is the epithelial lining of the gut tube derived from?

How does this affect the development of GIT-associated organs?

Answer 1

The epithelial lining is derived from endoderm

Other than the spleen, most GIT-associated organs are derived from endoderm

Question 2

How are the liver, gallbladder and pancreas formed?

Answer 2

They are outpocketings of endoderm in the cranial half of the duodenum

Question 3

What is duodenal papilla?

Answer 3

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

Question 4

During which week does the liver begin to develop?

How does it first appear?

Answer 4

week 3

it appears as an outpouching of endoderm from the foregut

This is the hepatic diverticulum (liver bud)

Question 5

What is the liver bud often called?

Answer 5

An endodermal plate

It is thickening of the endoderm at the cranial end of the duodenum

Question 6

What happens to the rapidly dividing cells in the hepatic diverticulum?

Answer 6

They penetrate the septum transversum

this goes on to form the diaphragm

Question 7

Why does the liver contain some cells of mesodermal origin?

Answer 7

The septum transversum is of mesodermal origin

Some of the mesodermal cells become encompassed within the liver

Question 8

What is formed from the connections between the hepatic diverticulum and the duodenum?

Answer 8

The bile duct

Question 9

What will endodermal cells develop into in the liver?

Answer 9

Endodermal cells develop into hepatocytes (parenchyma) of the liver

Question 10

What will be derived from the mesoderm of the septum transversum?

Answer 10

Haematopoietic cells

Kupffer cells

connective tissue

Question 11

What is the primary function of the liver in the developing foetus?

Why is this different in an adult?

Answer 11

Haematopoiesis - making blood cells

The liver of a foetus does not need to process metabolites from digestion as the mother does this

Question 12

Why does the function of the liver change after birth?

Answer 12

The baby must process the nutrients from the GI tract and make them usable

Question 13

What happens to haematopoiesis after birth?

Answer 13

It shifts to the bone marrow instead

Question 14

Why does the midgut herniate into the Vitelline duct?

Answer 14

The liver continues to rapidly expand, as does the small intestine

There is not enough space for both of them

Question 15

What happens when the liver can no longer be contained within the septum transversum?

Answer 15

It protrudes into the ventral mesentery and divides it into 2 parts:

1. falciform ligament
2. lesser omentum

Question 16

Where do the falciform ligament and lesser omentum run to and from?

Answer 16

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

Question 17

As the liver grows caudally, what is it in contact with?

What does this lead to?

Answer 17

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

Question 18

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

Answer 18

It differentiates into the visceral peritoneum, except on the cranial surface

Question 19

What happens to the cranial surface of the liver during differentiation of the mesoderm?

Answer 19

It becomes the bare area of the liver as it remains in contact with the septum transversum

Question 20

What forms around the margins of the bare area?

What are they formed from?

Answer 20

The peritoneum reflects to form anterior and posterior coronary ligaments

These are formed from mesoderm

Question 21

What are the triangular ligaments formed from?

Answer 21

Where the anterior and posterior coronary ligaments meet at the lateral edges of the liver

Question 22

What is the % of body weight taken up by the liver during week 10 of development?

How does this change after birth?

Answer 22

At week 10, the liver is 10% of total body weight

This decreases to 5% after birth

Question 23

When does the gallbladder form?

What does it form from?

Answer 23

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

Question 24

When does the foetus start producing bile?

What happens to it?

Answer 24

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

Question 25

What is the meconium?

Answer 25

The first bowel movement of the newborn

Question 26

What colour is the meconium and why?

Answer 26

It is dark green in colour This is due to the high concentration of bile

Question 27

What happens to bilirubin prior to birth?

Answer 27

Bilirubin crosses the placenta and is removed by the mother's circulation

Question 28

What happens to bilirubin after birth? Why is this necessary?

Answer 28

The liver conjugates bilirubin This makes it water-soluble It can then be excreted into the GI tract through the biliary system

Question 29

What is the enzyme needed to conjugate bilirubin?

Answer 29

Glucuronosyltransferase

Question 30

What happens if the immature liver does not contain enough glucuronosyltransferase?

Answer 30

Bilirubin cannot be sufficiently conjugated and secreted It accumulates - hyperbilirubinaemia This leads to neonatal jaundice

Question 31

What are the characteristic signs of neonatal jaundice?

Answer 31

Yellow skin and sclera

Question 32

What is the main complication of neonatal jaundice if it is untreated?

Answer 32

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

Question 33

How is neonatal jaundice treated?

Answer 33

Phototherapy (light therapy) Blue light is the most effective

Question 34

How can phototherapy prevent the risks of kernicterus?

Answer 34

Phototherapy oxidises bilirubin to a water-soluble form that can be easily excreted

Question 35

What causes biliary atresia?

Answer 35

Failure of the hepatic or bile duct to recanalise

Question 36

What happens during recanalisation of the hepatic and bile ducts?

Answer 36

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

Question 37

how many births are affected by biliary atresia?

Answer 37

1 in 15,000

Question 38

What is biliary atresia and what does it lead to?

Answer 38

The bile duct is narrowed, leading to a distended hepatic duct

Question 39

Why is biliary atresia often initially treated with phototherapy?

Answer 39

It presents with symptoms which are indistinguishable from neonatal jaundice

Question 40

How can biliary atresia be distinguished from neonatal jaundice?

Answer 40

As soon as phototherapy stops, the symptoms of jaundice will return

Question 41

What causes duplication of the gallbladder?

Answer 41

An extra endodermal outpocketing during weeks 5 and 6 This leads to formation of 2 gallbladders

Question 42

What are the symptoms of duplication of the gallbladder?

Answer 42

It is usually asymptomatic

Question 43

What does the pancreas initially develop as?

Answer 43

2 endodermal buds which fuse together These are the dorsal and ventral buds

Question 44

Which pancreatic endodermal bud develops first? How does it develop?

Answer 44

The dorsal bud appears in week 3 It is an outpocketing of the duodenum that extends into the dorsal mesentery

Question 45

Where does the ventral bud develop?

Answer 45

The ventral bud is a smaller diverticulum that is caudal to the developing gallbladder

Question 46

What happens as the stomach and duodenum rotate 90o to the endodermal buds?

Answer 46

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

Question 47

What do the dorsal and ventral buds give rise to?

Answer 47

The dorsal bud gives rise to the head, body and tail of the pancreas The ventral bud gives rise to the uncinate process

Question 48

What are the connective tissue and blood vessels surrounding the pancreas formed from?

Answer 48

Mesoderm

Question 49

What happens to the ductal systems when the dorsal and ventral buds fuse?

Answer 49

Their ductal systems become interconnected

Question 50

What is the main pancreatic duct formed from?

Answer 50

The distal portion of the dorsal pancreatic duct and ALL of the ventral pancreatic duct

Question 51

what is the accessory pancreatic duct formed from? What is significant about this?

Answer 51

Formed from the proximal portion of the dorsal pancreatic duct It is often obliterated during development

Question 52

Where does the main pancreatic duct enter the duodenum?

Answer 52

The main pancreatic duct and bile duct enter the duodenum at the Ampulla of Vater This is the major duodenal papilla

Question 53

How is the Ampulla of Vater controlled?

Answer 53

Contraction and relaxation of the sphincter of Oddi to allow secretions into the second part of the duodenum

Question 54

Where would the accessory pancreatic duct enter the duodenum?

Answer 54

at the minor duodenal papilla

Question 55

What condition results from a bilobed ventral pancreatic duct? How does this happen?

Answer 55

One lobe may migrate ventral to the duodenum and one love may migrate dorsally to surround the duodenum This leads to annular pancreas

Question 56

What is the consequence of annular pancreas?

Answer 56

It compresses the duodenum and causes gastrointestinal obstruction

Question 57

What is meant by ectopic pancreatic tissue?

Answer 57

Inappropriate differentiation of endodermal cells into pancreatic tissue This leads to pancreatic tissue being in places where it shouldn't

Question 58

Where is ectopic pancreatic tissue found?

Answer 58

Anywhere from the distal oesophagus to the tip of the primary intestinal loop It is most frequently in the duodenum or stomach muscosa

Question 59

What are the symptoms of ectopic pancreatic tissue?

Answer 59

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

Question 60

When does the spleen first appear? From what is it derived?

Answer 60

It appears in week 5 It is a mesenchymal condensation in the dorsal mesentery It is derived from mesoderm

Question 61

What is mesenchyme?

Answer 61

Undifferentiated mesoderm

Question 62

How does rotation of the stomach affect the spleen?

Answer 62

Rotation of the stomach brings the spleen over to the left-hand sidee

Question 63

How does the spleen divide the dorsal mesentery?

Answer 63

The gastrosplenic ligament is between the stomach and the spleen The lienorenal (splenorenal) ligament is between the spleen and kidney

Question 64

What causes an accessory spleen? How common are they?

Answer 64

Additional mesenchymal condensations may occur in the dorsal mesentery 10% of the population have an accessory spleen

Question 65

Where do accessory spleens usually form?

Answer 65

Near the hilum of the primary spleen

Question 66

What are they symptoms of an accessory spleen? Why is it important to recognise?

Answer 66

Usually asymptomatic It can affect the interpretation of medical images