Chapter 12:Cardiovascular Physiology

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

—increased Na+ & Ca2+ permeability

• If ↑, phase 4 spontaneous depolarization↑,

autorhythmicity ↑

• Ca2+ influx ↑, phase 0 amplitude & velocity ↑,

conductivity ↑

• Ca2+ influx ↑, Ca2+ release ↑, [Ca2+ ]i ↑, contractility ↑

Asymmetrical innervation of sympathetic nerve

Cardiac mechanisms of acetylcholine

Mechanisms of acetylcholine

—increased K+ permeability

• K+ outward ↑, |MRP| ↑, phase 4 spontaneous

depolarization ↓, autorhythmicity ↓

• Inhibition of Ca2+ channel, phase 0 amplitude &

velocity ↓, conductivity ↓

• Ca2+ influx ↓, [Ca2+ ]i ↓, contractility ↓

Cardiac effect of parasympathetic stimulation

Interaction of sympathetic and parasympathetic nerves

Predominance of autonomic nerves

Cardiovascular CenterA 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.

Figure 12-53

Characteristics of baroreceptors:Sensitive to stretching of the vessel walls

Proportional firing rate to increased stretching

Responding to pressures ranging from 60-180 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.

Figure 12-54

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

Figure 12-55

Reflex pathway

Click here to play theBaroreceptor Reflex Control

of Blood PressureFlash 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 theChemoreceptor Reflex Control

of Blood PressureFlash Animation

Humoral Regulation

• Vasoconstrictor agents• Vasodilator agents

Renin-angiotensin system

Juxtaglomerularcell

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

Effects Epinephrine Norepinephrine

Receptor α-adrenoceptor ++ +++

β-adrenoceptor ++ +

Heart heart rate + + (in vitro)－ (in vivo)

cardiac output +++ ±

Vessels constriction (skin, visceral) + +++

relaxation (SM, liver) － +++

total peripheral resistance ± +++

Blood pressure systolic +++ +++

diastolic ± ++

MAP + ++

Clinical application positive inotropic pressor agent

agent

Vasopressin (antidiuretic hormone, ADH)

Endothelium-derived vasoactive substances

•Vasodilator factors

PGI2--prostacyclin

EDRF, NO--endothelium-derived relaxing factor, nitric oxide

EDHF--endothelium-dependent hyperpolarizing factor

•Vasoconstrictor factorsEndothelin

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.