Regulation of Blood Pressure via Baroreceptor Reflexes

Blood volume and blood pressure drop in response to blood loss. When blood pressure falls, the baroreceptors are stretched less, and they send nerve impulses at a slower rate to the cardiovascular center.

In response, the cardiovascular center decreases parasympathetic stimulation of the heart by way of motor axons of the vagus nerves and increases sympathetic stimulation of the heart via cardiac accelerator nerves. Heart beats faster and more forcefully to increase cardiac output.

Another consequence of increased sympathetic stimulation is increased secretion of adrenaline and noradrenaline by the adrenal medulla which enhance both cardiac output and vasoconstriction. Vasoconstriction of the arterioles increases vascular resistance, whereas constriction of the veins increases venous return to the heart. All these events will help increase blood pressure.