Midgut

The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises the portion of the alimentary canal from the end of the foregut at the opening of the bile duct to the hindgut, about two-thirds of the way through the transverse colon.

Development

During development, the human midgut undergoes a rapid phase of growth in which the loop of midgut herniates outside of the abdominal cavity of the fetus and protrudes into the umbilical cord. This herniation is physiological (occurs normally). Later in development, the fetus's body catches up in size relative to the size of its own midgut and thereby creates adequate room in the abdominal cavity for the entirety of the midgut to reside. Thus, the midgut loops slips back out of the umbilical cord and the physiological hernia ceases to exist. This change coincides with the termination of the yolk sac and the counterclockwise rotation of the two limbs of the midgut loop around their combined central axis.