Circulation in the territory of the portal vein is made up of blood flows in the organs of this territory. Each of these organs has an intrinsic and extrinsic regulatory system. Portal hypertension results from a simultaneous increase of intrahepatic portal vascular resistances and blood flow rates. The rise in vascular resistance is due to a decrease of the intrahepatic vascular space consecutive to fibrosis and lesions of the liver cells. The cause of the increase in blood flow is imperfectly known. Physical, metabolic, hormonal and nervous factors may be responsible for these splanchnic circulatory changes, and they also produce changes in systemic haemodynamics.