Neural regulation of blood pressure - baroreceptor and chemoreceptor reflexes

• The nervous system regulates blood pressure with two reflex arcs: baroreceptor and chemoreceptor. ■ Baroreceptors (pressure) and chemoreceptors (chemical) are located in the carotid sinus and aortic arch. • Carotid sinus reflex helps maintain normal blood pressure in brain. • Baroreceptors are stimulated by the changes in the stretch of the carotid sinus wall; nerve impulses propagate from the baroreceptors over glossopharyngeal nerves to the CV center in the medulla oblongata. • Aortic reflex maintains general systolic blood pressure. • Baroreceptors in the wall of the ascending aorta and the aortic arch send impulses over vagus nerves. • If MABP drops, there is less stretch and fewer signals sent to the brain stem. • CV center sends out more sympathetic and fewer parasympathetic impulses. • Decrease in parasympathetic impulses increases heart rate and CO. • Increase in sympathetic impulses increases heart rate, myocardial contractility, venous tone, and CO. • Vasoconstriction of small arteries and arterioles increases SVR. • Increases in both CO and SVR cause MABP to rise back toward normal. • Reflexes also work in the opposite direction. • If MABP increases stretch then sensory nerve impulses increase. • Sympathetic impulses decrease; parasympathetic impulses increase. • Decreases in both CO and SVR cause MABP to lower back toward normal. • Receptors in carotid and aortic bodies detect chemical changes (O2, CO2, and H+') in blood level. • Such conditions as hypoxia (lowered O2), acidosis (increased H+), or hypercapnia (excess CO2) stimulate receptors to send impulses to CV center. • CV center increases sympathetic stimulation to arterioles and veins. • Increases in SVR, CO and venous tone cause MABP to rise back toward normal.

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