Characteristics of special circulations

Abstract Blood flow through a vascular bed is usually determined by the pressure gradient across it and diameter of precapillary resistance vessels. Special circulations have additional specific features blood control. Several organs control their supply autoregulation. Coronary linked to myocardial oxygen consumption, primarily metabolic mechanism. Increases in demand or decreases cause release vasodilator metabolites, which act on smooth muscle vessel relaxation hence increase flow. Cerebral regulated myogenic mechanism whereby increases transmural stretch muscle, responds contracting. Renal both extrinsic intrinsic mechanisms; sympathetic vasoconstriction afferent arterioles reduces renal response decrease effective circulating volume, mechanisms tubuloglomerular feedback, as well vasoactive metabolites from endothelium regulate intrinsically. Hepatic delivered via portal vein hepatic artery, amount varies these vessels reciprocally maintain constant total The pulmonary circulation receives entire cardiac output, passively actively. Pulmonary are highly distensible can accommodate without significant pressure.