What does the midgut give rise to?
- Small intestine, including most of the duodenum post bile duct entry
- Caecum and appendix
- Ascending colon
- Proximal 2/3 or transverse colon
Draw a diagram illustrating the position of the midgut in an embryo
What causes the midgut to make a loop?
It elongates enormously, and quickly runs out of space due to the large size of the developing liver
What does the loop made by the midgut have at its axis?
The superior mesenteric artery
What is the loop made by the midgut connected to?
The yolk sac
How is the midgut loop connected to the yolk sac?
By the vitelline duct
What are the limbs of the midgut loop called?
Cranial and caudal limbs
Label this diagram
- A - Cranial limb
- B - Superior mesenteric artery at axis
- C - Caudal limb
- D - Vitelline duct to yolk sac
What are the derivatives of the cranial limb?
- Distal duodenum
- Proximal ileum
What are the derivates of the caudal limb?
- Distal ileum
- Ascending colon
- Proximal 2/3 of transverse colon
What happens to the primary loop during the 6th week of development?
It elongates very rapidly
What happens to the liver during the 6th week of development?
It grows very rapidly
What is the problem with the rapid growth of both the liver and the primary loop?
The abdominal cavity is too small to accomodate both
What is the result of the abdominal cavity being too small too accomodate the primary loop and the liver?
What is physiological herniation?
Where the intestines herniate into the proximal umbilical cord, alongside the umbilical vessels
What are the stages in rotation of the midgut loop?
- First rotation
- Second rotation
By how much is the first rotation of the midgut loop?
By how much is the second rotation of the midgut loop?
What happens in the first rotation of the midgut loop?
During herniation into the umbilical cord, the midgut rotates around the axis formed by the SMA in a counter clockwise direction (cranial limb moves to back, caudal to the front)
Draw a diagram illustrating what happens in the first rotation of the midgut loop?
Does elongation of the small intestinal lumen continue during rotation?
What is the result of the elongation of the small intestinal loop continuing during rotation?
The jejunum and ileum form a number of coiled loops
What happens to the large intestine during rotation?
It lengthens, but does not participate in the coiling phenomenon
When does the second rotation of the midgut loop occur?
When it returns into the abdominal cavity, around week 10
In what direction does the second rotation of the midgut loop occur?
Turns 90 degrees counter-clockwise twice
Draw a diagram illustrating the second rotation of the midgut loop
In total, by how much does the midgut loop rotate?
270 degrees counter-clockwise
Which limb returns to the abdomen first?
The cranial limb
In what direction does the cranial limb move on return to the abdomen?
To the left hand side
What returns to the abdomen last following rotation?
The cecal bud