Arterial blood supply

The arterial blood supply of the jejunum and ileum is provided by the superior mesenteric artery (SMA) and its branches. The superior mesenteric artery enters the mesentery of the small intestine and gives off numerous jejunal and ileal arteries. Also, the terminal ileum receives arterial supply from another branch of the superior mesenteric artery - the ileocolic artery.

Venous drainage

The small intestine is drained by the vessels of the portal veinous system. The venous drainage of the jejunum and ileum occurs through small jejunal and ileal veins that carry blood to the superior mesenteric vein. The superior mesenteric vein merges with the splenic vein behind the head of the pancreas, and the blood drains into the hepatic portal vein. 

Overall, the superior mesenteric vein drains some parts of the stomach and greater omentum, small intestine, cecum, ascending colon and transverse colon. It is formed mainly by tributaries from the terminal ileum, cecum and vermiform appendix.