Extrinsic control of heart rate is exerted via the cardiopulmonary receptors, acting through sympathetic and parasympathetic branches of the autonomic nervous system. Receptors are located in the carotid sinus and aorta (baroreceptors), carotid and aortic bodies (chemoreceptors), the vena cavae and atria, the ventricles, the coronaries, the lungs, and elsewhere. The chemoreceptors are variously sensitive to blood PCO2, pH, PO2, while the baroreceptors are indirectly sensitive to blood pressure and/or volume. Such information reaches the cardiovascular center in the medulla through afferents, whereupon command signals are generated.
Intrinsic control of heart rate is generally of minor importance, being affected by ischemia, stretch, changes in K+ and Ca++ concentrations, and temperature.
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