1. Duodenum

    The first of four portions of the duodenum, the bulb, begins at the pylorus and transitions into the second portion, the descending part. The horizontal portion begins at the inferior duodenal flexure and sweeps to the left. The ascending portion transitions into the jejunum at the duodenojejunal flexure (ligament of Treitz) The blood supply to the duodenum is provided by the gastroduodenal, pancreaticoduodenal and supraduodenal arteries, which originate from the celiac axis and the superior mesenteric artery.