Lecture 19 - Development of GIT associated organs Flashcards
What are the organs derived from the foregut?
Liver
Gallbladder
Pancreas
where do the liver, gallbladder and pancreas develop from
These develop from diverticulum of the cranial half of the duodenum
Development of the Liver and Gallbladder. when does it occur?
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)
How does the bile duct form
connections between hepatic diverticulum and duodenum narrows to form bile duct
what are hepatocytes derived from?
endodermal cells
what are kupffer cells and connective tissue derived from?
derived from mesoderm of the septum transversum
How does the liver divide the ventral mesentery into 2 parts?
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
Peritoneum on the liver
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
Function of the Liver in Utero
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
Formation of the gallbladder
End of week 3, a ventral outgrowth of the bile duct forms the gallbladder and cystic duct
when does the liver start to produce bile
week 12
released into GI tract
As a result the first bowel movement of the newborn (meconium) is dark green in colour
what is the first bowel movement of a newborn called
meconium
Neonatal Jaundice
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)
What is kernicterus
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
Biliary Atresia
Hepatic and bile duct epithelium undergoes rapid proliferation and recanalisation
Failure of recanalisation leads to biliary atresia
1 in 15,000 births
symptoms of biliary atresia
initially indistinguishable from neonatal jaundice but do not respond to phototherapy
Duplication of Gallbladder
Common congenital malformation
Usually asymptomatic
Caused by an extra endodermal outpocketing during weeks 5 and 6
Triple gallbladders have also been reported
Development of the Pancreas
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
How do the different parts of the pancreas form?
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
Formation of Pancreatic Ducts
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
Main pancreatic duct - where does it enter the duodenum?
Main pancreatic duct (plus bile duct enters into duodenum at major duodenal papilla (Ampulla of Vater)
Where does the minor pancreatic duct enter the duodenum?
minor duodenal papilla
Annular Pancreas
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
Ectopic Pancreatic Tissue
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
Development of the Spleen - what is it derived from?
not endoderm like other organs
mesoderm
appears in week 5 as a mesenchymal condensation in the dorsal mesentery
how does the spleen assume its position?
The rotation of the stomach brings the spleen over the left hand side
What is the dorsal mesentery between the stomach and the spleen called?
gastrosplenic ligament
What is the dorsal mesentery between the kidney and the spleen called?
linorenal ligament
Accessory Spleen
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
