Hepatic arterial resistance Rha is high, with a large pressure drop from aorta to hepatic vein, and its changes will affect Qha. Rha can be modified by hormones and nerves (extrinsic factors). The composition of portal blood and the gastrointestinal hormones seem to be the most important determinants of the extrinsic regulation of Qhep. During postprandial hyperosmolarity, Qhep is increased and a hepatic arterial vasodilation is observed with secretion of secretin, pentagastrin, cholecystokinin-pancreozymin, and vasoactive intestinal peptide. Glucagon also increases Qhep, mainly by increasing Qpv secondary to an intestinal vasodilatation.
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