Cardiovascular Physiology Qiang XIA (夏强), MD & PhD Department of Physiology Room C518, Block C, Research Building, School of Medicine Tel:

Regulation of Cardiovascular Activities Lecture Outline Nervous Regulation Humoral Regulation Autoregulation

Nervous Regulation

Innervation of cardiovascular system

Nervous regulation of the circulation

Cardiac mechanisms of norepinephrine

Mechanisms of norepinephrine —increase Na + & Ca 2+ permeability I f , phase 4 spontaneous depolarization , autorhythmicity  Ca 2+ influx , phase 0 amplitude & velocity , conductivity  Ca 2+ influx , Ca 2+ release , [Ca 2+ ] i , contractility 

Asymmetrical innervation of sympathetic nerve

Cardiac mechanisms of acetylcholine

Mechanisms of acetylcholine —increase K + & decrease Ca 2+ permeability K + outward , |MRP| , phase 4 spontaneous depolarization , autorhythmicity  Inhibition of Ca 2+ channel, phase 0 amplitude & velocity , conductivity  Ca 2+ influx , [Ca 2+ ] i , contractility 

Cardiac effect of parasympathetic stimulation

Interaction of sympathetic and parasympathetic nerves

Predominance of autonomic nerves

Cardiovascular Center A collection of functionally similar neurons that help to regulate HR, SV, and blood vessel tone

Vasomotor center Located bilaterally mainly in the reticular substance of the medulla and of the lower third of the pons –Vasoconstrictor area –Vasodilator area –Cardioinhibitor area – dorsal nuclei of the vagus nerves and ambiguous nucleus –Sensory area – tractus solitarius

Vasomotor center

–Reticular substance of the pons –Mesencephalon –Diencephalon –Hypothalamus –Cerebral cortex –Cerebellum Higher cardiovascular centers

Baroreceptor Reflexes Arterial baroreceptors –Carotid sinus receptor –Aortic arch receptor Afferent nerves (Buffer nerves) Cardiovascular center: medulla Efferent nerves: cardiac sympathetic nerve, sympathetic constrictor nerve, vagus nerve Effector: heart & blood vessels

Baroreceptor neurons function as sensors in the homeostatic maintenance of MAP by constantly monitoring pressure in the aortic arch and carotid sinuses.

Characteristics of baroreceptors:  Sensitive to stretching of the vessel walls  Proportional firing rate to increased stretching  Responding to pressures ranging from mmHg  Receptors within the aortic arch are less sensitive than the carotid sinus receptors

The action potential frequency in baroreceptor neurons is represented here as being directly proportional to MAP.

Baroreceptor neurons deliver MAP information to the medulla oblongata’s cardiovascular control center (CVCC); the CVCC determines autonomic output to the heart. i.e., MAP is above homeostatic set point i.e., reduce cardiac output

Reflex pathway

Click here to play the Baroreceptor Reflex Control of Blood Pressure Flash Animation

Typical carotid sinus reflex

Maintaining relatively constant arterial pressure, reducing the variation in arterial pressure Physiological Significance

Other Cardiovascular Reflexes Click here to play the Chemoreceptor Reflex Control of Blood Pressure Flash Animation

Humoral Regulation Vasoconstrictor agents Vasodilator agents

Renin-angiotensin system

Juxtaglomerular cell Renin

–Constricts resistance vessels –Acts upon the adrenal cortex to release aldosterone –Stimulates the release of vasopressin –Facilitates norepinephrine release from sympathetic nerve endings –Stimulates thirst centers within the brain Physiological effects of angiotensin II

Epinephrine & Norepinephrine Sources Epinephrine---- adrenal medulla Norepinephrine---- adrenal medulla sympathetic nerves

Catecholamines Norepinephrine Epinephrine

EffectsEpinephrineNorepinephrine Receptor  -adrenoceptor  -adrenoceptor++ + Heartheart rate+ + (in vitro) － (in vivo) cardiac output+++ ± Vesselsconstriction (skin, visceral) relaxation (SM, liver) － +++ total peripheral resistance ± +++ Blood pressuresystolic diastolic ± ++ MAP + ++ Clinical applicationpositive inotropic pressor agent agent

Vasopressin (antidiuretic hormone, ADH)

Endothelium-derived vasoactive substances Vasodilator factors PGI 2 --prostacyclin EDRF, NO--endothelium-derived relaxing factor, nitric oxide EDHF--endothelium-dependent hyperpolarizing factor Vasoconstrictor factors Endothelin

Atrial natriuretic peptide (ANP) Produces natriuresis and diuresis Decreases renin release Reduces total peripheral resistance via vasodilatation Decreases heart rate, cardiac output

Autoregulation Definition: Intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure, independent of any neural or humoral influences

The End.