Mean Arterial Pressure Control

Mean Arterial Pressure Control 2 mechanisms exist to monitor and regulate changes in MAP (mean arterial pressure): 1) Baroreceptor reflex—more important for short-term control of blood pressure - Arterial baroreceptors in the carotid sinus sense and respond to acute increases or decreases in arterial pressures - Arterial baroreceptors in the aortic arch respond to acute increases, but not decreases in arterial pressure. 2) RAA (renin angiotensin aldosterone) system—more important for long-term control of blood pressure. For example, how would the body respond to an acute hypotensive episode? 1) Baroreceptor reflex responds within seconds: Acute ↓ in MAP →↓ afferent signals sent from the carotid sinus baroreceptors via glossopharyngeal nerve (CN IX) to the brain stem medulla →↓ in parasympathetic activity via the efferent vagus nerve to the heart, with a simultaneous ↑ in sympathetic outflow from the nucleus of the solitary tract to the heart and vasculature → - ↑ Heart rate (chronotropic effect) - ↑Myocardial contractility (inotropic effect) ∴↑ stroke volume - ↑ AV conduction velocity (dromotropic effect) - ↑ TPR (total peripheral resistance) ∴compensatory↑ of mean arterial pressure toward normal Recall: MAP = CO*TPR, and CO = HR * SV CO=cardiac output, HR=heart rate, SV=stroke volume 2) RAA (renin angiotensin aldosterone) system senses the the acute drop in blood pressure but takes minutes-hours-days to kick into gear: ↓ MAP →↓ renal blood flow is sensed by the juxtaglomerular apparatus →↑ renin →↑ angiotensin II → - Angiotensin II is a potent vasoconstrictor that increases total peripheral resistance. - Angiotensin II also stimulates release of aldosterone → stimulates renal sodium retention and subsequent renal fluid reabsorption to help maintain total blood volume in an attempt to preserve stroke volume, cardiac output, and mean arterial pressure.