S3.2 Development Of The Midgut And Hindgut Flashcards
What does the primary intestinal loop comprise?
The midgut has an opening at the unmbilicus where it is connected to the yolk sac via the viteline duct.
The midgut makes a loop with the SMA at its axis and cranial and caudal limbs
What is physiological herniation?
The abdominal cavity is too small to accommodate elongation of the primary loop and liver growth, so the intestines herniate into umbilical cord
Describe rotation of the midgut loop
During herniation into the umbilical cord, the midgut rotates around the axis formed by the SMA in an anti-clockwise direction.
It rotates 90 degrees, then 180 degrees.
What problems can occur with incomplete rotation?
If midgut makes only one 90 degree rotation - Left sided colon
What problems can occur with reversed rotation?
Midgut makes one 90 degree rotation clockwise
Transverse colon passes posterior to the duodenum. (Can wrap around and occlude it)
What is meckels diverticulum?
A pouch in the ileum due to a remnant of the yolk sac, as the viteline duct persists.
This can produce ectopic gastric mucosa that may then produce gastric acid, causing ulceration.
Rule of 2’s
What is a viteline cyst?
The vitelline duct forms fibrous strands at either end.
What is a viteline fistula?
There is direct communication between the umbilicus and the intestinal tract. This results in faecal matter coming out of the umbilicus.
What is recanalisation?
The process of restoring a lumen which may have been previously obliterated
What is gastroschisis?
Failure of closure of the abdominal wall during embryo folding, leaving the gut tube and its derivatives outside the body cavity with no covering.
What is an omphalocoele?
The persistence of physiological herniation. A part of the gut tube fails to return to the abdominal cavity following its normal herniation into the umbilical cord. Covered by a reflection of the amnion
How is the hindgut formed?
Via cloacal partitioning
The urorectal septum grows down into the cloaca, dividing it in to the urogenital sinus anteriorly and the anorectal canal posteriorly.
The superior part of the anal canal is Hindgut derived, the inferior is endoderm derived, what separates this?
The pectinate/dentate line
Describe the features above the pectinate/dentate line
IMA
Pelvic nerve S2-4
Visceral innervation so only sensitive to stretch
Columnar epithelia
Describe the features below the pectinate/dentate line
Pudendal artery
Pudendal nerve S2-4
Somatic innervation so sensitive to temperature touch and pain
Stratified squamous epithelia
