The portal vein is formed by the union of which veins?

• A. Splenic and Superior Mesenteric
• B. Inferior Mesenteric and Splenic
• C. Left Gastric and Splenic
• D. Superior Mesenteric and Left Gastric

Answer: (A)

The portal vein is formed by the meeting of two major contributors: the splenic vein and the superior mesenteric vein, typically behind the neck of the pancreas. The splenic vein drains the spleen and also collects blood from short gastric and left gastroepiploic veins, while the superior mesenteric vein drains most of the midgut structures (small intestine, cecum, ascending and part of the transverse colon) and receives tributaries like the right gastroepiploic and pancreaticoduodenal veins. These two veins come together to form the portal vein, which then carries blood to the liver via the porta hepatis.

The other veins mentioned are tributaries to the portal system rather than forming it. The left gastric vein drains into the portal system but does not form the portal vein. The inferior mesenteric vein commonly drains into the splenic vein (or, less commonly, near the join) and thus contributes to the portal system rather than forming it.