Midgut: physiological herniation and rotation !

Process

The gut grows so fast that it moves out into the umbilical cord, turns around its artery and returns to the abdomen around week 10.

Updated 2026-11-01

See it in 3D: Jejunum · Ileum · Cecum · Appendix · Superior mesenteric artery · Ascending colon · Transverse colon

What it is

The midgut forms a U-shaped loop supplied by the superior mesenteric artery and attached at its apex to the vitelline duct. In week 6 it moves out into the umbilical cord (physiological herniation), because the abdomen is too small for the growing liver and kidneys. It rotates 270° counterclockwise around the artery and returns to the abdomen around week 10. Errors in this process explain malrotation, volvulus, omphalocele and Meckel diverticulum.

Structure

Cranial limb of the loop: distal duodenum, jejunum and proximal ileum.
Caudal limb of the loop: distal ileum, cecum, appendix, ascending colon and proximal two-thirds of the transverse colon.
The axis of the whole process is the superior mesenteric artery, which runs in the mesentery of the loop.

Step by step

Week 5: the U-shaped midgut loop has a cranial and a caudal limb, with the superior mesenteric artery as its axis and the vitelline duct at its apex.
Week 6: the cranial limb lengthens rapidly and the loop moves out into the umbilical cord.
During herniation the loop turns 90° counterclockwise: the cranial limb moves to the right and the caudal limb to the left.
The cecal bud appears on the caudal limb and marks the future cecum and appendix.
Week 10: the loop returns to the abdomen and turns a further 180°, for 270° in total.
The proximal jejunum returns first and occupies the left side; the cecum returns last, in the right upper quadrant.
The cecum descends to the right iliac fossa and the ascending colon is completed.
The mesenteries of the ascending and descending colon fuse with the posterior wall, which makes them secondarily retroperitoneal.

Clinical notes

Absent or incomplete rotation: malrotation with Ladd bands and a risk of midgut volvulus.
Reversed (clockwise) rotation: the transverse colon passes behind the duodenum and the superior mesenteric artery.
Failure of the herniated loop to return: omphalocele.
Persistent vitelline duct: Meckel diverticulum, fistula, cyst or fibrous band.
Undescended cecum: a subhepatic appendix, which makes appendicitis harder to recognise.

Test yourself

Think of the answer, then tap the question to see it.

How many degrees, and in which direction, does the midgut rotate?

270° counterclockwise, viewed from the front, around the superior mesenteric artery.

Why does the gut move into the umbilical cord in week 6?

Because it grows very fast while the abdominal cavity is small and largely filled by the developing liver and kidneys.

Which part of the gut returns to the abdomen last?

The cecum, which first lies below the liver and then descends to the right iliac fossa.

Which malformation results if the herniated loop fails to return?

An omphalocele: viscera outside the abdomen at the base of the cord, covered by a membrane.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

Acute appendicitis

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Embryology, Midgut (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Gastrointestinal (StatPearls Publishing (NCBI Bookshelf), 2023); Intestinal Malrotation (Nemours KidsHealth, 2021).

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Representative model, for educational purposes only.