Development of the GI tract part 2 Flashcards
What does the midgut give rise to?
Small intestine (most of duodenum)
Caecum and appendix
ascending colon
2/3 of transerse colon
What is the primary intestinal loop?
Midgut elongates enormously and runs out of space
makes a loop thats connected to the yolk sac by the vitelline duct and has cranial and caudal limbs, sma as axis
When is physiological herniation?
6th week
What happens in physiological herniation?
primary intestinal loop growth is rapid
liver grows rapidly
abdominal cavity is too small to acommodate both
intestines hernate into umbilical cord
What are the steps of midgut rotation?
What happens after rotation?
descent of caecal bud
What happens if there is incomplete rotation of the midgut?
makes only 1 90 degree rotation- left sided colon
makes on 90 degree rotation clockwise- transverse colon passes posterior to the duodenum
What are the risks associated with midgut defects?
Strangualtion and ischaemia
What is herniation?
Protrusion of a viscus through a hole
What happens to remnants of the yolk sac?
vitelline duct persists resulting in vitelline cyst, vitelline fistula and meckels divericulum
What is meckels diveriticulum?
Where does recanalisation occur?
oesphagus, bile duct, small intesting
Why does recanalisation occur?
Cell grwoth becomes so rapid that the lumen is completely obliterated
What happens if recanalisation is unsuccessful?
Atresia- lumen obliterated or stenosis- lumen narrowed
mainly in duodenum
What is a pyleric stenosis?
Hypertrophy of the circular muscle in the region of the pyloric sphincter
-not a reacanalisation failure
causes projectile vomiting
What is gastroschisis?
Failure of closure of the abdominal wall during folding of the embryo
Leaves gut tube and derivatives outside the body cavity
What is omphalocoele (exophalos)
Persistance of the physiological herniation
Differs from umbilical hernia because hernia has skin and subcutaneous tissue
How is the anal canal divided?
Pectinate line into histologically superior and inferior parts
What is the proctodeum?
Junction between two embryonic germ layers
What is above and below the pectinate line?
Where do the different parts of the gut hurt?
What are some hindgut abnormalities?
What structures of the midgut and hindgut have fused mesentaries?
– Duodenum
– Ascending colon
– Descending colon
– Rectum (no peritoneal covering in distal 1/3)
