The liver receives a dual blood supply coming from the hepatic artery and portal vein. The portal venous system collects nutrient-rich blood from the gastrointestinal tract and its accessory organs and carries it to the liver.

The portal vein provides around 70-75% of the blood directed to the liver. It contains blood that is poor in oxygen but rich in nutrients absorbed from the small intestine. In contrast, the systemic arterial blood supply occurs via the hepatic artery, and it constitutes around 25-30% of the blood flow. Therefore, the liver is also supplied by the portal vein.

The main hepatic portal vein arises behind the neck of the pancreas. It is formed by the confluence of the superior mesenteric vein and splenic vein. Also, the inferior mesenteric vein may join either the superior mesenteric or the splenic vein.

The main hepatic portal vein passes behind the duodenum, running along the free border of the lesser omentum through the hepatoduodenal ligament. It is typically located behind the proper hepatic artery and the common bile duct within the ligament.

At the hilum of the liver, the main portal vein divides into two branches:

Left portal vein - flows towards the umbilical fissure and gives off branches to segments 1, 2, 3, and 4;
Right portal vein - it is relatively short and divides into two branches after entering the liver:
- Right anterior branch - supplies segments 5 and 8; very rarely, it also supplies segment 1;
- Right posterior branch - supplies segments 6 and 7.

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Portal venous system