The inferior mesenteric vein is a venous blood vessel which drains a small portion of the transverse colon, the descending colon, and the rectum. It receives oxygen-poor blood from the left colic vein, the sigmoid veins, the left and right rectal vein, and the middle and inferior rectal veins, all of which drain these parts of the large intestine as they get together to form this thick venous vessel of the digestive system.
The inferior mesenteric vein begins in the cavity of the true pelvis as the superior rectal vein. Then it runs upwards, parallel to the inferior mesenteric artery, and joins the splenic vein, emptying the blood it carries into it. The splenic in turn joins the superior mesenteric vein to form the hepatic portal vein. Thus, this blood vessel is part of the hepatic portal system.
The inferior mesenteric is located behind the peritoneum and, as it ascends, it forms a small arch, whose convexity is directed to the left. After receiving the left colic vein, it swerves to the right, passing immediately to the left of the duodenojejunal flexure under the pancreas, where it finally joins the splenic vein. In some cases, it does not unite with the splenic but empties its content directly into the portal vein.
Below, a diagram and drawing of the inferior mesenteric vein.
