Embryology of the GI Tract Flashcards
At what point during embryonic development does the primordial gut tube form?
The 4th week
What is the primordial gut derived from?
The endoderm lining the yolk sac
What seals the primordial gut tube?
Cranial End - Oropharyngeal Membrane
Caudal End - Cloacal Membrane
What is the oesophagus derived from?
The cranial part of the primitive gut tube
What is the trachea-oesophageal septum?
The ridge that divides the foregut tube into the trachea and oesophagus
What happens if the trachea-oesophageal septum deviates incorrectly?
There is incomplete separation of the laryngo-tracheal tube which results in oesophageal atresia and trachea-oesophageal fistula
What structure is the stomach formed from?
The foregut
How does the stomach grow differentially to the size and location it has in an adult?
- Differential growth creates the greater and lesser curves
- The stomach rotates 90 degrees around its longitudinal axis
- The stomach undergoes an anterio-posterior rotation to create the final adult position
How is the lesser sac created?
It is created when the stomach rotates, pulling the dorsal mesentery to the left and creating the lesser sac
What structures form the duodenum?
The caudal part of the foregut and cranial part of the midgut
What is the blood supply to the duodenum?
Coeliac Trunk and Superior Mesenteric Artery
At what point in embryonic development does the liver first appear?
The liver primordium bud appears in the middle of the 3rd week
Where does the liver bud grow?
Into the septum transversum plate between the pericardial cavity and yolk sac
What structure forms the bile duct?
The connection between the liver and foregut narrows to form the bile duct
From what structure are the gall bladder and cystic duct formed?
The ventral outgrowth from the bile duct
At what point during development is the spleen formed/
5th week
From what structure is the spleen derived from?
Mesoderm
At what point during development does the spleen start its lymphoid function?
Week 23
What is the pancreas formed from?
From 2 buds which grow from the endodermal lining of the duodenum in week 5
What structures fuse to form the main pancreatic duct?
Ventral Duct + Distal Part of Dorsal Duct
What structure can the proximal part of the dorsal duct form?
The accessory duct
What cause an annular pancreas?
The ventral bud failing to migrate around the duodenum correctly
What are the consequences of an annular pancreas?
It may cause duodenal stenosis and accessory pancreatic tissue
What structures will be formed from the cephalic end of the primary intestinal loop?
Distal duodenum, jejunum and proximal ileum
What structures will be formed from the caudal end of the primary intestinal loop?
The distal ileum, caecum, appendix, ascending colon and the proximal 2/3 of the transverse colon
How and when does the midgut rotate?
The primary intestinal loop rotates 90 degrees anti-clockwise around the axis of the superior mesenteric artery in the 6th week of development
What is physiological herniation of the midgut?
When the gut tube herniates into the extraembryonic cavity in the umbilical cord to make room for the gut tube to grow
At what point do the herniated loops retract?
During the 10th week when there is more space in the abdominal cavity
What is omphalocele?
Herniation of abdominal viscera through an enlarged umbilical ring and failed retraction of the umbilical ring
What is gastrochisis?
Herniation of abdominal contents directly through the body wall into the amniotic cavity. The contents are not covered by peritoneum or amnion and they herniate through a week spot to the right of the umbilicus
What consequences can arise from remnants of the vitelline duct?
It forms Meckel’s diverticulum and may form fistula or vitelline cyst/ligament
What structures make up the hindgut?
Distal 1/3 transverse colon, descending colon, sigmoid colon, rectum and anal canal
What structures does the endoderm of the hindgut form?
The lining of the bladder and urethra
What is the cloaca?
The endoderm lined cavity with surface ectoderm at its ventral border
At what point in development does the cloacal membrane rupture opening the hindgut?
End of week 7
