Coronary blood flow regulated by

Ans. is 'c' i.e., Local muscle action and reflexesRegulation of coronary blood flow mainly occurs by chemical regulation through autoregulation.Regulation of coronary blood flowRegulation of coronary flow occurs by two mechanisms : ?1) Chemical regulation (Autoregulation)Regulation of coronary blood flow occurs through local intrinsic regulation, i.e., autoregulation, most likely through the production of vasodilating metabolites in response to minimal degree of ischemia. The vasodilatory chemical stimuli are low PO2, High PCO2, H+, K+, lactic acid, ADP AMP and adenosine. Chemical regulation (autoregulation) of coronary blood flow is far more impoant than neural regulation.2) Neural regulationCoronary aeries are supplied by autonomic sympathetic and parasympathetic system. Coronary aeries have both alpha and beta sympathetic (adrenergic receptors), with the beta receptors predominating. Beta receptor stimulation produces vasodilation whereas alpha receptor stimulation produces vasoconstriction. There are relatively few parasympathetic (vagal) fibers supplying the coronary aeries. The direct effect of these fibers is vasodilatation; But indirect effect causes vasoconstriction and predominates. Indirect effect is the result of decrease in formation of vasodilator metabolites due to decrease in hea rate and cardiac contractility.