The remarkable flexibility of the circulation in adjusting blood flow through different tissues according to their metabolic needs while at all times preserving the arterial blood pressure and hence adequate perfusion of vital structures such as the brain and heart is achieved by the autonomic control of the peripheral vascular system.
Because of the constancy of arterial blood pressure, the blood flow through a tissue is determined by the caliber of the vessels which nourish it. The caliber of these vessels is a function of vascular smooth muscle tone, a complex property implying a state of partial contraction which is sustained in part by intrinsic factors and modified by extrinsic factors such as autonomic nervous stimuli and chemical agents.1 The discovery by Bohr and Sobieski2 in normal plasma of a small, heat-stable, cationic component which is able to contract isolated vascular smooth muscle and the revival of
Edis AJ, Shepherd JT. Autonomic Control of the Peripheral Vascular System. Arch Intern Med. 1970;125(4):716-724. doi:10.1001/archinte.1970.00310040140020