Portal hypertension
- Mechanism
If blood cannot pass through the liver, pressure backs up into the gut veins, causing fluid in the belly, varices and a big spleen.
What it is
Portal hypertension is raised pressure in the portal venous system. Resistance can be before the liver (portal vein thrombosis), inside it (cirrhosis, schistosomiasis, sinusoidal obstruction) or after it (hepatic vein obstruction, right heart failure). Cirrhosis is by far the most common cause. Raised resistance combines with increased portal inflow from splanchnic vasodilation to produce ascites, portosystemic shunts, congestive splenomegaly and hepatic encephalopathy.
Structure
- Varices: dilated tortuous submucosal veins of the distal esophagus and gastric cardia.
- Spleen: enlarged, firm, with congested red pulp, fibrosis and sometimes Gamna-Gandy bodies (iron and calcium deposits).
Step by step
- Scar, regenerating nodules and contracted stellate cells raise intrahepatic resistance.
- Sinusoidal endothelium makes less nitric oxide and more vasoconstrictors, adding resistance.
- Splanchnic arteries dilate (nitric oxide and other mediators), so more blood enters the portal system.
- Portal pressure rises; collateral veins open between portal and systemic circulations.
- Fluid leaks from sinusoids into the peritoneum, worsened by low albumin and sodium retention: ascites.
- Spleen congests and enlarges, trapping platelets; gut toxins bypass the liver: encephalopathy.
Where the block is
| Level | Examples | Point to remember |
|---|---|---|
| Prehepatic | Portal vein thrombosis, splenic vein thrombosis, extrinsic compression | Liver itself may be normal; ascites less common |
| Intrahepatic presinusoidal | Schistosomiasis, portal-tract fibrosis, nodular regenerative hyperplasia | Liver function usually preserved |
| Intrahepatic sinusoidal | Cirrhosis of any cause | The most common cause |
| Intrahepatic postsinusoidal | Sinusoidal obstruction syndrome | Zone 3 congestion and necrosis |
| Posthepatic | Budd-Chiari syndrome, constrictive pericarditis, right heart failure | Large tender liver with congestion |
Clinical notes
- Hematemesis from varices, abdominal distension from ascites, splenomegaly, confusion.
- Ascites can become infected without an obvious source: spontaneous bacterial peritonitis.
Test yourself
Think of the answer, then tap the question to see it.
Which portosystemic anastomosis causes life-threatening bleeding in portal hypertension?
The esophagogastric one (left gastric vein to azygos system), which forms varices of the distal esophagus and gastric cardia.
Why does schistosomiasis cause portal hypertension with good liver function?
Eggs trapped in portal venules cause periportal pipe-stem fibrosis: the block is presinusoidal and the parenchyma is largely spared.
What links portal hypertension to thrombocytopenia?
Congestive splenomegaly sequesters platelets (hypersplenism); low thrombopoietin from the failing liver adds to it.
What are the four main consequences of portal hypertension?
Ascites, portosystemic shunts with varices, congestive splenomegaly and hepatic encephalopathy.
Elsewhere in DurgiPedia
Connections
Microorganisms1
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Portal Hypertension (StatPearls (NCBI Bookshelf), 2025); Bleeding esophageal varices: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.