inferior mesenteric artery

The IMA arises from the anterior abdominal aorta at approximately the L3 vertebral level, roughly 3-4 cm above the aortic bifurcation. It supplies the hindgut derivatives: distal 1/3 of transverse colon, descending colon, sigmoid colon, and upper rectum (down to the pectinate line via superior rectal artery). Major branches include the left colic artery, sigmoid arteries, and superior rectal artery (continuation of IMA), which anastomoses with the middle rectal artery (from internal iliac) to supply the rectum. The marginal artery of Drummond connects IMA branches with the middle colic artery (from SMA), providing collateral circulation. The splenic flexure is a watershed zone between SMA and IMA territories, making it vulnerable to ischemic colitis during hypoperfusion states (e.g., shock, atherosclerosis). Similarly, the rectosigmoid junction is a watershed area between IMA and internal iliac artery supply. Clinically, IMA occlusion or atherosclerosis can cause ischemic colitis, presenting with abdominal pain, bloody diarrhea, and thumbprinting on imaging. During abdominal aortic aneurysm (AAA) repair, the IMA may be ligated, usually well-tolerated due to collateral flow via the marginal artery and arc of Riolan, but can cause ischemic colitis if collaterals are insufficient. Embryologically, the hindgut (supplied by IMA) gives rise to structures innervated by parasympathetic fibers from S2-S4 (pelvic splanchnic nerves), unlike the midgut (SMA territory) innervated by vagus nerve.