The inferior mesenteric artery provides the blood supply to the third segment on the left side of the transverse colon. It also supplies the sigmoid colon with blood. Near the lower part of the body, the rectal arteries provide blood to this section of the intestines. This boundary is important for surgeons to understand, since the blood supply from the arteries and the way the veins drain do undergo a change in this area. The endodermal portion of the colon gets its blood from the sigmoid artery; this branches off of the inferior mesenteric artery. In contrast, the ectodermal section of the colon receives its blood supply from the rectal arteries; these are branches of the internal iliac artery.