Lecture 19 - Development of GIT associated organs

Question 1

What are the organs derived from the foregut?

Answer 1

Liver
Gallbladder
Pancreas

Question 2

where do the liver, gallbladder and pancreas develop from

Answer 2

These develop from diverticulum of the cranial half of the duodenum

Question 3

Development of the Liver and Gallbladder. when does it occur?

Answer 3

week 3
the liver appears as an out-pocketing of the future duodenum – hepatic diverticulum (liver bud)

This contains rapidly proliferating cells that penetrate the septum transversum (future diaphragm)

Question 4

How does the bile duct form

Answer 4

connections between hepatic diverticulum and duodenum narrows to form bile duct

Question 5

what are hepatocytes derived from?

Answer 5

endodermal cells

Question 6

what are kupffer cells and connective tissue derived from?

Answer 6

derived from mesoderm of the septum transversum

Question 7

How does the liver divide the ventral mesentery into 2 parts?

Answer 7

Liver continues to rapidly expand (link to herniation of midgut)

Becomes too large to be contained within the septum transversum – protrudes into ventral mesentery

This divides the ventral mesentery into 2 parts:
Falciform ligament
Lesser omentum

Question 8

Peritoneum on the liver

Answer 8

mesoderm on liver surface differentiates into visceral mesoderm - except on cranial surface - becomes bare area

Around margins of bare area, peritoneum reflects - coronary ligament

Coronary ligament ultimately ends at the lateral edges of the liver - left and right triangular ligaments

Question 9

Function of the Liver in Utero

Answer 9

at week 10 the liver has 10% body weight
5% at birth
reason for a large liver in the foetus is it’s importance in haematopoiesis - at birth shifts to bone marrow

Question 10

Formation of the gallbladder

Answer 10

End of week 3, a ventral outgrowth of the bile duct forms the gallbladder and cystic duct

Question 11

when does the liver start to produce bile

Answer 11

week 12
released into GI tract
As a result the first bowel movement of the newborn (meconium) is dark green in colour

Question 12

what is the first bowel movement of a newborn called

Answer 12

meconium

Question 13

Neonatal Jaundice

Answer 13

Prior to birth, bilirubin crosses the placenta and is removed by the mother’s circulation
After birth, the liver conjugates bilirubin which is then excreted into the GIT through the biliary system

In 60% full term infants - immature liver insufficient glucuronosyltransferase to conjugate bilirubin – hyperbilirubinaemia (jaundice)

Yellow skin and sclera (whites of eyes)

Question 14

What is kernicterus

Answer 14

complication of untreated neonatal jaundice

Excess unconjugated bilirubin crosses the blood-brain barrier and causes brain damage

Phototherapy oxidises bilirubin to a water soluble form that can be easily excreted by the newborn and does not contribute to kernicterus

Blue light is the most effective

Question 15

Biliary Atresia

Answer 15

Hepatic and bile duct epithelium undergoes rapid proliferation and recanalisation

Failure of recanalisation leads to biliary atresia

1 in 15,000 births

Question 16

symptoms of biliary atresia

Answer 16

initially indistinguishable from neonatal jaundice but do not respond to phototherapy

Question 17

Duplication of Gallbladder

Answer 17

Common congenital malformation

Usually asymptomatic

Caused by an extra endodermal outpocketing during weeks 5 and 6

Triple gallbladders have also been reported

Question 18

Development of the Pancreas

Answer 18

Pancreas initially develops as 2 endodermal buds that fuse together

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

The ventral bud appears as a smaller diverticulum caudal to the developing gallbladder

As duodenum rotates 90° clockwise (as stomach rotates) the ventral bud carried dorsally along with bile duct

Question 19

How do the different parts of the pancreas form?

Answer 19

Ventral pancreatic bud comes to lie posterior to dorsal bud

Fuse in 6th week

Dorsal bud gives head, body and tail of pancreas

Ventral bud forms uncinate process

Connective tissue and blood vessels formed from surrounding mesoderm

Question 20

Formation of Pancreatic Ducts

Answer 20

Main pancreatic duct formed from distal portion of dorsal pancreatic duct and ALL of the ventral pancreatic duct

Accessory pancreatic duct formed from proximal portion of dorsal pancreatic duct

Accessory pancreatic duct may be obliterated during development

Question 21

Main pancreatic duct - where does it enter the duodenum?

Answer 21

Main pancreatic duct (plus bile duct enters into duodenum at major duodenal papilla (Ampulla of Vater)

Question 22

Where does the minor pancreatic duct enter the duodenum?

Answer 22

minor duodenal papilla

Question 23

Annular Pancreas

Answer 23

ventral pancreatic bud can be bilobed
In this case, one lobe may migrate ventral to the duodenum and one may migrate dorsally to surround the duodenum – annular pancreas
This can compress the duodenum causing gastrointestinal obstruction

Question 24

Ectopic Pancreatic Tissue

Answer 24

Inappropriate differentiation of endodermal cells into pancreatic tissue

Can be found in areas ranging from distal oesophagus to tip of primary intestinal loop

Most frequently in duodenum or stomach mucosa

Usually asymptomatic

Large lesions may cause obstruction, ulceration or haemorrhage

Question 25

Development of the Spleen - what is it derived from?

Answer 25

not endoderm like other organs
mesoderm
appears in week 5 as a mesenchymal condensation in the dorsal mesentery

Question 26

how does the spleen assume its position?

Answer 26

The rotation of the stomach brings the spleen over the left hand side

Question 27

What is the dorsal mesentery between the stomach and the spleen called?

Answer 27

gastrosplenic ligament

Question 28

What is the dorsal mesentery between the kidney and the spleen called?

Answer 28

linorenal ligament

Question 29

Accessory Spleen

Answer 29

Additional mesenchymal condensations may occur in the dorsal mesentery and form accessory spleens – 10% population

These usually form near the hilum of the primary spleen

Usually asymptomatic but can affect interpretation of medical images and are an important variant for surgeons to be aware of