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

Explanation

## Formation of the Portal Vein **Key Point:** The portal vein is a major venous channel that carries nutrient-rich, oxygen-poor blood from the gastrointestinal tract and spleen to the liver for processing and detoxification. ### Anatomy of Portal Vein Formation The portal vein is formed **behind the neck of the pancreas** by the confluence of two major tributaries: 1. **Superior Mesenteric Vein (SMV)** — drains the small intestine, cecum, ascending colon, and transverse colon 2. **Splenic Vein** — drains the spleen, pancreas, and parts of the stomach and colon ### Major Tributaries of the Portal Vein | Tributary | Drainage Territory | Confluence Point | |-----------|-------------------|------------------| | **Superior Mesenteric Vein** | Small bowel, cecum, ascending & transverse colon | Forms portal vein with splenic vein | | **Splenic Vein** | Spleen, pancreas, left colon, fundus of stomach | Forms portal vein with SMV | | **Left Gastric Vein** | Lesser curvature of stomach, lower esophagus | Joins portal vein directly | | **Right Gastric Vein** | Lesser curvature of stomach | Joins portal vein directly | | **Cystic Vein** | Gallbladder | Joins portal vein or right portal branch | | **Superior Rectal Vein** | Upper rectum | Joins SMV | **High-Yield:** The portal vein enters the liver at the porta hepatis and divides into right and left branches. It is NOT formed by hepatic veins — hepatic veins drain blood OUT of the liver into the inferior vena cava. **Mnemonic:** **SMV + Splenic = Portal Vein**. Remember: the portal vein is an **afferent** vessel (bringing blood TO the liver), while hepatic veins are **efferent** vessels (draining blood FROM the liver). **Clinical Pearl:** Portal hypertension (pressure > 12 mmHg) can develop from obstruction at any point in the portal system. The SMV and splenic vein confluence is a critical anatomical landmark in portal vein thrombosis and surgical portosystemic shunt procedures. [cite:Standring Anatomy 42e Ch 65]