Portal hypertension is defined as increased portal venous pressure, with a hepatic venous pressure gradient greater than 5 mmHg.[3][4] Normal portal pressure is 1¨C4 mmHg; clinically insignificant portal hypertension is present at portal pressures 5¨C9 mmHg; clinically significant portal hypertension is present at portal pressures greater than 10 mmHg.[5] The portal vein and its branches supply most of the blood and nutrients from the intestine to the liver.[6]

Reference
Wiki: Portal hypertension