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ANATOMY OF THE LARGE INTESTINE

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Because of its embryologic development from both the midgut and hindgut, the colon has two main sources of blood supply: the superior mesenteric (1) and the inferior mesenteric arteries (2). The superior mesenteric artery (1) supplies the right colon, the appendix, and small intestine. The middle colic artery (3) is the most prominent branch of the superior mesenteric artery. It arises after the pancreaticoduodenal vessels (see Chapter 5). The middle colic artery branches into a right and left division. The right division anastomoses with the right colic (4) and the ileocolic (5) arteries. The left branch communicates with the marginal artery of Drummond (6). The middle and right colic and ileocolic arteries are doubly ligated near their origin when a right colectomy is performed for malignancy. The ileocolic artery reaches the mesentery of the appendix from beneath the terminal ileum. Angulation or obstruction of the terminal ileum should be avoided following the ligation of the appendiceal artery (7) in the presence of a short mesentery.

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The inferior mesenteric artery arises from the aorta just below the ligament of Treitz. Its major branches include the left colic (8), one or more sigmoid branches (9, 10), and the superior hemorrhoidal artery (11). Following ligation of the inferior mesenteric artery at its origin, the viability of the colon is maintained through the marginal artery of Drummond (6) by way of the left branch of the middle colic artery.

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The third blood supply to the large intestine arises from the middle and inferior hemorrhoidal vessels. The middle hemorrhoidal vessels (12) arise from the internal iliac (hypogastric) (13), either directly or from one of its major branches. They enter the rectum along with the suspensory ligament on either side. These are relatively small vessels, but they should be ligated.

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The blood supply to the anus is from the inferior hemorrhoidal (14) vessels, a branch of the internal pudendal artery (15). In low-lying lesions wide excision of the area is necessary with ligation of the individual bleeders as they are encountered.

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The venous drainage of the right colon parallels the arterial supply and drains directly into the superior mesenteric vein (1). The inferior mesenteric vein, in the region of the bifurcation of the aorta, deviates to the left and upward as it courses beneath the pancreas to join the splenic vein. High ligation of the inferior mesenteric vein (16) should be carried out before extensive manipulation of a malignant tumor of the left colon or sigmoid in order to avoid the vascular spread of tumor cells.

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The right colon can be extensively mobilized and derotated to the left side without interference with its blood supply. The mobilization is accomplished by dividing the avascular lateral peritoneal attachments of the mesentery of the appendix, cecum, and ascending colon. Blood vessels of a ...

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