Descending colon

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Divisions, features, neurovasculature and lymphatic drainage of the large intestine.

The descending colon is a segment of the large intestine positioned within the left paracolic gutter of the posterolateral abdominal wall. It extends from the left hypochondriac region and runs through the left flank to reach the left iliac fossa. Beginning at the left colic flexure proximally, it descends vertically and becomes continuous with the sigmoid colon distally.

Developmentally, the descending colon arises from the hindgut along with the distal third of transverse colon, sigmoid colon, rectum and superior portion of anal canal.

In adults, the descending colon measures about 25–30 cm. It is a retroperitoneal organ, with its anterolateral surface covered by parietal peritoneum that attaches it to the posterior abdominal wall. It runs anterior to the lateral border of the left kidney and in about a third of people, the distal portion of the descending colon has a short mesentery.

Similar to other segments of the colon, the descending colon has epiploic (omental) appendices, teniae coli, and haustrations. Histologically, much like other parts of the colon, the descending colon is composed of four distinct layers: mucosa, submucosa, muscularis and serosal layers. The mucosal layer is lined by simple columnar epithelium and has intestinal glands with goblet cells and absorptive cells.

The descending colon is supplied by the left colic artery, a branch of the inferior mesenteric artery, and drained by the inferior mesenteric vein. Functionally, the descending colon continues the process of water and electrolyte absorption from digestive materials and further compacts its contents, ultimately leading to the formation of feces.