Organ
Ascending (fourth) part of the duodenum
Duodenal ascent toward the mobile jejunum
High-yield
The duodenojejunal flexure marks the usual boundary used to describe upper gastrointestinal bleeding. The inferior mesenteric vein is a useful nearby landmark on its left.
Overview
After crossing the spine, the duodenum turns upward on the left side of the aorta. This fourth segment ends at the duodenojejunal flexure, usually near L2, where the bowel becomes the mesenteric jejunum. The suspensory muscle and surrounding connective tissue support the transition.
Reference facts
- Location
- Rises left of the aorta from the horizontal duodenum toward the L2 region.
- Parts
- The terminal duodenal segment and its bend into the jejunum are supported at the duodenojejunal flexure.
- Blood supply
- Branches of the inferior pancreaticoduodenal and proximal jejunal arteries provide superior mesenteric inflow.
- Innervation
- Autonomic fibers travel in superior mesenteric plexus branches; parasympathetic input is vagal.
- Venous/Lymphatic drainage
- Venous return reaches the superior mesenteric system; lymph passes through regional nodes toward superior mesenteric nodes.
- Relations
- Close to the left psoas and renal vessels posteriorly; the pancreatic body and transverse mesocolon are superior, and the inferior mesenteric vein lies near the left side of the flexure.
- Function
- Transfers duodenal contents into the jejunum as digestion and absorption continue.
Clinical correlation
An internal hernia near the duodenojejunal region can trap small bowel within a peritoneal recess. The resulting obstruction may occur without an external abdominal-wall swelling.
Frequently asked questions
Where is the ascending (fourth) part of the duodenum located?
The ascending (fourth) part of the duodenum lies rises left of the aorta from the horizontal duodenum toward the L2 region.
What does the ascending (fourth) part of the duodenum do?
Transfers duodenal contents into the jejunum as digestion and absorption continue.
What are the parts of the ascending (fourth) part of the duodenum?
The terminal duodenal segment and its bend into the jejunum are supported at the duodenojejunal flexure.
What is the blood supply of the ascending (fourth) part of the duodenum?
Branches of the inferior pancreaticoduodenal and proximal jejunal arteries provide superior mesenteric inflow.