the anatomy of the organ which acts as a reservoir of blood

Sympathetic Nervous System.

The liver is a significant blood reservoir, and 50% of its blood volume may be mobilized by nerve stimulation (Greenway & Lautt, 1989). Denervation experiments have shown that the sympathetic nervous system is not involved in basal arterial tone in the liver (Mathie & Blumgart, 1983). Hepatic sympathetic nervous stimulation causes hepatic arterial vasoconstriction and reduced blood flow, which appears secondary to an autoregulatory response (Greenway & Stark, 1971). Sensory denervated rats and pigs have a diminished arterial buffer response on partial occlusion of the PV (Ishikawa, 1995). Portal pressure increases as a result of an increase in portal venous resistance, but portal flow does not decrease unless there is a decrease in intestinal or splenic blood flow caused by simultaneous sympathetic stimulation of these vascular beds. Although the HA contains both α-adrenergic and β-adrenergic receptors, the portal venous system is believed to contain only α-receptors (Richardson & Withrington, 1981). At low doses, epinephrine causes hepatic and mesenteric arterial vasodilation, whereas at high doses, vasoconstriction occurs in the hepatic arterial and portal venous vascular beds and in the mesenteric circulation (Greenway & Stark, 1971; Richardson & Withrington, 1981).