As a blood vessel, the inferior mesenteric vein (IMV) drains blood away from the descending colon, rectum, and sigmoid, which are all parts of the large intestine.

The IMV branches off the portal vein, which also branches into the superior mesenteric vein. The IMV also has its own branches. These include the sigmoid vein, which drains the sigmoid, and the left colic vein, which drains the descending colon.

As a whole, the inferior mesenteric vein drains away deoxygenated blood from the colon, where it will eventually be returned to the right ventricle and atrium in the heart, as well as the pulmonary veins in the lungs.

The descending colon is essential during the final phase of digestion. Here, any remaining substances are broken down and water is removed. The colon then processes the remaining waste products into feces, which is then moved through the sigmoid and downward toward the rectum. For this process, an ongoing supply of blood is necessary.

The IMV should not be confused with the inferior mesenteric artery, which delivers oxygen-rich blood to specific areas of the large intestine.