Portal Vein
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Direct answer
The portal vein, about 8 cm long, is formed behind the neck of the pancreas at about the level of L2 by the union of the superior mesenteric and splenic veins. It ascends behind the first part of the duodenum and runs in the free edge of the lesser omentum, where it lies behind and between the bile duct on the right and the hepatic artery on the left, and divides into right and left branches at the porta hepatis. It carries nutrient-rich blood from the gut, spleen, pancreas and gallbladder to the liver.
What you must remember
- Formation: superior mesenteric and splenic veins behind the neck of the pancreas; the left gastric vein joins the portal vein itself, while the inferior mesenteric vein usually joins the splenic vein.
- Relations at the free edge: the portal triad — bile duct right and in front, proper hepatic artery left and in front, portal vein behind; the epiploic foramen opens onto this triad from the right, with the inferior vena cava further back.
- Termination: divides into right and left branches at the porta hepatis; the left branch is joined by the ligamentum teres and the ligamentum venosum.
- Portacaval anastomoses: lower oesophagus, anorectal region, paraumbilical region, retroperitoneal veins of the gut, and the bare area of the liver — the classical five sites.
- Effects of portal hypertension: oesophageal varices with haematemesis, splenomegaly, ascites, caput medusae and rectal varices.
- Special features: the vein is valveless, and it normally delivers a larger share of the blood entering the liver than the hepatic artery does.
Common confusion
The portal vein is formed behind the neck of the pancreas, not at the porta hepatis where it divides. In the free edge of the lesser omentum the bile duct lies right and anterior, the artery left and anterior, and the vein behind both. Distinguish true rectal varices, which are portosystemic shunts, from ordinary haemorrhoids.
Exam-focused takeaway
For theory, draw the formation and course with the triad in the hepatoduodenal ligament, then chart the five anastomotic sites with their clinical signs. In viva, expect the tributaries, the relations at the free edge, and the anatomy behind variceal bleeding. For spotters, identify the triad at the porta hepatis and explain where a portosystemic shunt is created.
Frequently asked questions
How and where is the portal vein formed?
By the union of the superior mesenteric and splenic veins behind the neck of the pancreas, at about the level of L2.
What are its relations in the lesser omentum?
In the free edge, it lies behind and between the bile duct on the right and the proper hepatic artery on the left, with the inferior vena cava further behind.
Enumerate the portacaval anastomoses.
The lower oesophagus, anorectal region, paraumbilical region, retroperitoneal veins of the gut, and the bare area of the liver.
Why do oesophageal varices bleed?
Left gastric (portal) veins anastomose with azygos (systemic) veins at the lower oesophagus; in portal hypertension they dilate into submucosal varices that rupture easily.
How long is the vein and does it have valves?
About 8 cm, and valveless, so portal pressure is transmitted throughout its length.
What is caput medusae?
Dilated paraumbilical veins radiating from the umbilicus, formed when portal blood escapes through the ligamentum teres to the epigastric veins.