The portal vein is formed by the union of which two vessels?

Explanation

## Formation of the Portal Vein **Key Point:** The portal vein is formed behind the neck of the pancreas by the union of the superior mesenteric vein (SMV) and the splenic vein. This occurs at the level of L2 vertebra. ### Anatomical Formation The portal vein is formed by: 1. **Superior mesenteric vein (SMV)** — drains the small intestine, cecum, ascending colon, and proximal two-thirds of the transverse colon 2. **Splenic vein** — drains the spleen, pancreas, and left side of the colon These two veins unite behind the neck of the pancreas to form the main portal vein, which then ascends in the hepatoduodenal ligament. ### Major Tributaries of the Portal Vein | Tributary | Drainage Territory | |-----------|-------------------| | Superior mesenteric vein | Small intestine, cecum, ascending and proximal transverse colon | | Splenic vein | Spleen, pancreas, left colic vessels | | Left gastric vein | Stomach, lower esophagus | | Right gastric vein | Stomach | | Cystic vein | Gallbladder | | Para-umbilical veins | Umbilical region | **High-Yield:** The portal vein carries nutrient-rich, oxygen-poor blood from the GI tract to the liver. It is a key landmark in hepatobiliary surgery and imaging. **Mnemonic:** **SMV + SV = PV** (Superior Mesenteric Vein + Splenic Vein = Portal Vein) **Clinical Pearl:** Portal hypertension develops when portal vein pressure exceeds 12 mmHg, leading to esophageal varices, splenomegaly, and ascites. [cite:Standring Anatomy 42e Ch 77]