Session 3: Embryology Flashcards
What does the midgut give rise to?
- Small intestine
- Caecum
- Appendix
- Ascending colon
- Proximal 2/3 transverse colon
What occurs after the midgut elongates and runs out of space?
Makes a loop that
- Has the superior mesenteric artery as its axis
- Is connected to the yolk sac by vitelline duct
- Has cranial and caudal limbs
What is physiological herniation?
6th
- Growth of primary intestinal loop is very rapid
- Liver is also growing rapidly
- Abdominal cavity is too small to accommodate both and intestines herniate into the umbilical cord
How many rotations does the mid gut undergo?
3 rotations
What occurs if the midgut loop only does one 90 degree rotation?
Results in a left sided colon
What occurs with a reversed rotation?
The midgut loop make one 90 degree rotation clockwise which result in the transverse colon passing posteriorly to the duodenum
What are the risks associated with midgut defects?
Immobile structures can become mobile which can result in twisting. This can lead to strangulation and ischaemia
What are abnormalities associated with the vitelline duct?
Vitellline duct can persist resulting in:
- Meckel’s diverticulum which can contain ectopic or pancreatic tissue
- Vitelline cyst where the vitelline duct forms fibrous strands
- Vitellline fistula where there is a direct ocommunication between the umbilicus and intestinal tract
What are the rules of 2 associated with meckel’s diverticulum?
- 2% of the population
- 2 feet from the illeocaecal valve
- Ususlaly detected in under 2s
- 2:1 ratio in male:female
Why do some gut structures require recanalisation?
Cell growth can be so rapid that the lumen is partially or completely obliterated due to the growth being faster than the tube formation. Recanalisation helps to restore the lumen
What are the effect of unsuccessful recanalisation?
Atresia - lumen obliterated
Stenosis - lumen narrowed
What is the site of common atresia and stenosis in the gut?
Duodenum
- Most likely cause is incomplete canalisation
- Vascular accidents also contribute
What is pyloric stenosis?
Hypertrophy of circular muscle in the region of the pyloric sphincter and not a recanlisation failure. This causes a narrowing of the exit from the stomach causing projectile vomiting
What is gastroschisis?
Failure of closure of the abdominal wall during folding of the embryo. This leaves the gut tube and derivatives outside the body cavity.
-Can be resolved after delivery
What is omphalocoele?
-Persistence of physiological herniation
