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Hepatic portal vein

Main duct or vein · Foregut Midgut Hindgut

Formed behind the neck of the pancreas at L1-L2 by union of the splenic and superior mesenteric veins, it ascends about 8 cm, first behind the first part of the duodenum and then in the free edge of the lesser omentum, posterior to the bile duct (right) and hepatic artery proper (left) and in front of the epiploic foramen and IVC, dividing at the porta hepatis into right and left branches. It is valveless and carries nutrient-rich, partly deoxygenated blood from the entire gut, spleen and pancreas, so everything absorbed passes through the liver before reaching the systemic circulation.

Traced from the start

  1. Inferior mesenteric veinShort gastric and left gastro-omental veins
  2. Jejunal, ileal, ileocolic, right colic and middle colic veinsRight gastro-omental and pancreaticoduodenal veins
  3. Oesophageal veins (lower third)
  4. Splenic veinSuperior mesenteric veinLeft gastric (coronary) vein
  5. Hepatic portal vein

Detail

Formation
Splenic vein plus superior mesenteric vein behind the pancreatic neck, L1-L2
Length
About 8 cm
Direct tributaries
Left and right gastric, cystic, paraumbilical and posterior superior pancreaticoduodenal veins
Flow
About 1000-1200 mL/min: 70-75% of hepatic blood flow and about half of hepatic oxygen delivery
Pressure
5-10 mmHg; hepatic venous pressure gradient normally 1-5 mmHg
Valves
None

When it goes wrong

Raised sinusoidal resistance in cirrhosis (or prehepatic portal vein thrombosis, or posthepatic Budd-Chiari syndrome)

Portal hypertension: hepatic venous pressure gradient above 5 mmHg; 10 mmHg or more is clinically significant (varices form) and 12 mmHg or more is the threshold for variceal bleeding and ascites

Portal vein thrombosis (cirrhosis, hepatocellular carcinoma, thrombophilia, neonatal umbilical sepsis)

Prehepatic portal hypertension with varices and splenomegaly but preserved liver function; chronic cases show cavernous transformation, a mass of collateral veins replacing the vein

Pringle manoeuvre: clamping the free edge of the lesser omentum

Occludes the portal vein and hepatic artery together to control liver bleeding; bleeding that continues must come from the hepatic veins or IVC

Oral drug absorbed from the gut into the portal vein

First-pass hepatic metabolism cuts bioavailability (glyceryl trinitrate, propranolol, morphine), which sublingual and rectal routes partly bypass

Practise this structure

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