Midgut and hindgut: the mesenteric arteries and the colon

1. Superior mesenteric artery

The superior mesenteric artery supplies the midgut: from the second part of the duodenum to two-thirds of the way along the transverse colon. Jejunal and ileal arteries leave its left side; the colic arteries leave its right side.

Surgeon’s corner: Acute mesenteric ischaemia (embolus usually a few cm after the origin) spares the first jejunal loops and the transverse colon beyond the middle colic artery: a typical pattern at laparotomy.

2. The colic branches

Three branches run to the right colon: the middle colic artery to the transverse colon, the right colic artery (inconstant) to the ascending colon, and the ileocolic artery to the caecum, the terminal ileum and the appendix.

Surgeon’s corner: In a right hemicolectomy for cancer the ileocolic and right colic vessels are tied at their origin from the superior mesenteric vessels, with the lymph nodes along them (central vascular ligation).

3. The appendix and its artery

The appendicular artery is a branch of the ileocolic artery. It runs in the free edge of the mesoappendix to the tip of the appendix. It is an end artery: there is no back-up.

Surgeon’s corner: Because it is an end artery, thrombosis in appendicitis leads to gangrene and perforation. At appendicectomy, sealing the mesoappendix controls this vessel; find the base where the taeniae coli converge.

4. Inferior mesenteric artery: the hindgut

The inferior mesenteric artery leaves the aorta at L3, about 4 cm above the bifurcation, and supplies the distal third of the transverse colon down to the upper rectum: left colic artery, sigmoid arteries and the superior rectal (anorectal) artery.

Surgeon’s corner: In anterior resection the inferior mesenteric artery is tied high (oncological) or just below the left colic (preserving flow to the descending colon). The inferior mesenteric vein runs separately, beside the duodenojejunal flexure.

5. Watersheds and veins

Where two arterial territories meet, the blood supply is weakest: the splenic flexure (between middle and left colic) and the rectosigmoid junction. The veins follow the arteries and drain into the portal vein: superior mesenteric vein, splenic vein and inferior mesenteric vein.

Surgeon’s corner: Ischaemic colitis typically hits the splenic flexure. Anastomoses must have good blood supply on both sides: check the cut edge bleeds (or use fluorescence angiography).