Anatomy of the duodenum
The fourth part of the duodenum is the shortest segment, and represents the location where the duodenum turns upwards (after passing the left side of the abdominal aorta) and then forwards to become intraperitoneal (embedded in the peritoneum).
The last part of the duodenum is suspended from the retroperitoneum by the suspensory ligament (of Treitz) and the point at which it becomes the Jejunum is demarcated by the Duodenojejunal (DJ) flexure.
