Sectional Presentation of the Duodenojejunal Flexure

Description

Arising at the left upper quadrant, the duodenojejunal flexure (flexura duodenojejunalis) is presented in an anterior sectional plane where the fourth part of the duodenum turns superiorly and to the left to become proximal jejunum. Proximal to the junction, the duodenal mucosa shows broader, more leaflike plicae circulares that become taller and more regular as the lumen transitions into jejunum. Posterior to this angle lies the retroperitoneal duodenum, while the jejunal segment becomes intraperitoneal and drifts inferiorly with the root of the mesentery. Clinically, this junction is a fixed landmark because the suspensory muscle of the duodenum (ligament of Treitz) anchors the flexure to the right crus of the diaphragm and adjacent connective tissue near the celiac region. Fixation matters. It explains why proximal small bowel obstruction can present with marked gastric and duodenal dilation up to the duodenojejunal junction, and it orients the surgeon during exploration of malrotation, internal hernia near the paraduodenal fossa, or trauma where identifying the transition from retroperitoneal duodenum to mobile jejunum guides exposure. The change in mucosal folding also reinforces functional anatomy, since dense plicae in the jejunum correlate with absorptive surface area compared with the more variable folds of the distal duodenum. Use this sectional view in gastrointestinal anatomy and embryology teaching to anchor the concept of the duodenojejunal angle as the divider between foregut and midgut territory and to pair with radiology discussions of an upper GI series assessing the position of the DJ flexure in suspected malrotation. It also fits operative atlases describing a Kocher maneuver and subsequent identification of the ligament of Treitz when mobilizing the duodenum and proximal jejunum. Anatomical accuracy verified by SciePro's Medical Advisory Board.