Transverse Descending And Sigmoid Colon

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The transverse colon ends at the spleen, where the colon bends as the left colic (splenic) flexure (Figure 10-2A). The colon continues vertically down the left wall of the abdomen as the descending colon. The parietal peritoneum covers only the anterior surface of the descending colon, and thus the descending colon is considered a retroperitoneal structure.

A depression between the lateral surface of the descending colon and the abdominal wall is known as the left paracolic gutter. Branches of the left colic artery supplying the descending colon enter the bowel on its medial surface. As such, it is possible to surgically mobilize the descending colon by cutting the peritoneum along the left paracolic gutter without injuring major vessels or lymphatics.

The transverse colon is part of both the midgut (supplied by left and middle colic arteries, branches of the superior mesen-

teric artery) and the hindgut (supplied by left colic arteries, branches of the inferior mesenteric artery). The descending colon also receives its vascular supply mainly from the left colic artery (branch of the inferior mesenteric artery) (Figure 10-2B).

VThe marginal artery (of Drummond) is an arterial anastomosis between the superior and inferior mesenteric arteries. The marginal artery courses within the mesentery and parallels the ascending, transverse, and descending colon. The anastomosis is so complete that during the repair of an aortic aneurism, the inferior mesenteric artery often will not be regrafted to the aorta because the marginal artery will supply blood to the hindgut via the superior mesenteric artery. ▼

Near the left iliac fossa, the descending colon continues as the sigmoid colon, which is an intraperitoneal structure. The vascular supply of the sigmoid colon is via sigmoid arteries from the inferior mesenteric artery.

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