Hepatic circulations in animals
The hepatic blood supply from the hepatic artery and portal vein is governed by hepatic arterial vascular resistance, the arterial tone in the vascular beds of the gastrointestinal tract, pancreas, and the spleen and the intrahepatic portal venous vascular resistance.
The total hepatic blood flow in humans, cats and dogs contributes about 70 to 75% of the total hepatic blood flow.
Sympathetic nerve stimulation increases hepatic arterial and portal venous tone. Since the liver, is a major blood reservoir, sympathetic stimulation rapidly mobilizes large amounts of blood for redistribution to vital organs under stress conditions.
Epinephrine decreases hepatic artery flow and total hepatic blood volume. The hepatic vasculature contains both alpha and beta-adrenergic receptors.
The hepatic arterial vascular bed exhibits relatively weak local control of its blood flow through both myogenic and metabolic types of autoregulation.
The portal system lacks such intrinsic local control mechanisms. A partial reciprocity between the hepatic artery and the portal vein helps maintain total liver blood flow constant.
- Vasopressin has three effects on the liver circulation-
- Hepatic arterial constriction,
- Mesenteric vasoconstriction, and
- Dilator action on intrahepatic portal resistance vessels. Angiotensin II causes marked vasoconstriction of both hepatic arterial and portal beds.