A patient was admitted with symptoms of bowel obstruction. Fuher examination revealed that the obstruction was caused by the nutcracker-like compression of the bowel between the superior mesenteric aery and the aoa. The compressed bowel is MOST likely to be:

The superior mesenteric aery crosses over the third pa of the duodenum, and the aoa is posterior to the third pa of the duodenum. If something causes these vessels to become enlarged, they can crush the duodenum, and food will not be able to pass through the duodenum. This is often called the "nutcracker effect", and it is only seen in the third pa of the duodenum.