As a blood vessel, the inferior mesenteric vein (IMV) drains blood away from the descending colon, rectum, and sigmoid. As a whole, the various parts of the colon are also called "the large intestines." The IMV branches off of the portal vein, which also branches into the superior mesenteric vein. Also, the IMV has tributaries that include the sigmoid vein and the left colic vein. The descending colon is essential in the final process 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 from the colon and into the rectum. As such, an ongoing supply of blood remains essential. 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. As such, the IMV should not be confused with the inferior mesenteric artery (IMA). The IMA delivers oxygenated blood to specific areas of the large intestine.