Final answer:
The first rotation of the midgut occurs in the abdomen during embryonic development, rotating 90 degrees counterclockwise around the superior mesenteric artery, positioning the duodenum in its characteristic C-shaped curve around the pancreas.
Step-by-step explanation:
The first rotation of the midgut occurs as the embryonic gut tube rotates around the axis of the superior mesenteric artery. This rotation is a critical period during embryonic development, and it takes place within the abdomen of a developing fetus. Initially, as the midgut elongates, it herniates out into the umbilical cord because there is not enough space in the abdominal cavity. During the first rotation, the midgut rotates 90 degrees counterclockwise around the axis of the superior mesenteric artery. This rotation positions part of the small intestine, specifically the duodenum, to eventually move into a retroperitoneal position creating a C-shaped curve around the head of the pancreas after the midgut returns to the abdominal cavity.