Organ
Horizontal (third) part of the duodenum
Duodenal crossing beneath the mesenteric vessels
High-yield
From anterior to posterior at the crossing: superior mesenteric vessels, horizontal duodenum and aorta. The inferior vena cava is also a posterior relation farther to the right.
Overview
The third duodenal segment crosses from right to left in front of the lumbar spine and great vessels. The superior mesenteric artery and vein pass anterior to it as they enter the mesentery. This arrangement places the bowel within the interval between the aorta and superior mesenteric artery.
Reference facts
- Location
- Mostly retroperitoneal, crossing the midline near L3 from the right side toward the left.
- Parts
- Begins after the inferior duodenal bend and turns upward into the fourth segment.
- Blood supply
- Predominantly inferior pancreaticoduodenal branches of the superior mesenteric artery, communicating with the wider duodenal network.
- Innervation
- Superior mesenteric autonomic pathways, including vagal parasympathetic fibers and visceral afferents.
- Venous/Lymphatic drainage
- Venous return reaches superior mesenteric channels; lymph passes through regional pancreaticoduodenal and superior mesenteric nodes.
- Relations
- Mesenteric root and superior mesenteric vessels anteriorly; aorta and vena cava posteriorly; pancreatic uncinate region superiorly.
- Function
- Continues intestinal transit, mixing, digestion and absorption between the descending and ascending duodenum.
Clinical correlation
Loss of tissue cushioning the aortomesenteric interval, sometimes after substantial weight loss, can contribute to symptomatic duodenal compression. A narrow vascular angle alone does not establish superior mesenteric artery syndrome.
Frequently asked questions
Where is the horizontal (third) part of the duodenum located?
Mostly retroperitoneal, crossing the midline near L3 from the right side toward the left.
What does the horizontal (third) part of the duodenum do?
Continues intestinal transit, mixing, digestion and absorption between the descending and ascending duodenum.
What are the parts of the horizontal (third) part of the duodenum?
The parts of the horizontal (third) part of the duodenum are the begins after the inferior duodenal bend and turns upward into the fourth segment.
What is the blood supply of the horizontal (third) part of the duodenum?
Predominantly inferior pancreaticoduodenal branches of the superior mesenteric artery, communicating with the wider duodenal network.