The ascending (fourth) part of the duodenum is short, about 2.5-5 cm, running up and to the left of the aorta to reach the lower border of the pancreas at L2. There it turns forward to join the jejunum at the duodenojejunal flexure. It is held in place by the suspensory muscle of the duodenum.
| Location | Left of the aorta and vertebral column, from L3 to L2, ending at the duodenojejunal flexure |
|---|---|
| Parts |
|
| Nerve Supply | Vagus nerve; Superior mesenteric plexus |
| Blood Supply | Inferior pancreaticoduodenal arteries; First jejunal artery |
| Venous drainage |
|
| Lymphatic drainage |
|
Carries chyme from the duodenum to the jejunum.
Its position at the end of the duodenal C-loop is used on contrast studies to rule out malrotation: in normal anatomy the flexure lies to the left of the spine at about the level of the pylorus. Peritoneal recesses next to this part can trap loops of bowel, causing paraduodenal hernia.
Internal hernia of small bowel into a peritoneal fossa beside the ascending duodenum, causing intermittent or acute obstruction.
Abnormal rotation of the midgut in which the duodenojejunal flexure lies right of the midline, predisposing to volvulus.
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