Portal venous system

The portal venous system drains blood from all the abdominal viscera. The distal tributaries of this system correspond to the arterial blood supply to form, eventually, the inferior mesenteric vein and the superior mesenteric vein. The inferior mesenteric vein ascends to the left of the duodenojejunal flexure to join the splenic vein behind the pancreas. The superior mesenteric vein joins the splenic vein behind the neck of the pancreas at the transpyloric plane to form the portal vein which ascends behind the first part of the duodenum, behind the bile duct and hepatic artery into the porta hepatis. The portal vein divides into right and left branches which eventually drain into lobules of the liver and then reform as radicals of the hepatic vein through which they empty into the inferior vena cava (Fig. 12.2). Communications exist between the portal venous system and the systemic venous system at the oesophageal branches of the left gastric vein and the oesophageal veins of the azygos system in the thorax. A rise in

Common bile duct

Common bile duct

Pancreas

Duodenal-jejunal flexure

Ampulla of vater

Superior mesenteric vessels

Pancreas

Duodenal-jejunal flexure

Ampulla of vater

Superior mesenteric vessels

Figure 12.1. Anatomy of the duodenum and pancreas.

pressure in this system forms oesophageal varices. Communications also form between the superior haemorrhoidal branch of the inferior mesenteric vein and inferior haemorrhoidal veins, between tributaries in the mesentery and mesocolon and retroperitoneal veins, between portal branches in the liver and veins of the abdominal wall through veins passing along the falciform ligament to the umbilicus and between portal branches in the liver and veins of the diaphragm around the bare area of the liver.

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