autoregulation of the cardiovascular system

7/27/2019 Autoregulation of the Cardiovascular System

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Autoregulation of the Cardiovascular

System

Local Control of Organ Blood Flow

Endothelium-Derived Relaxing Factor

(Nitric Oxide)

Baroreceptor Reflex

Renin-Angiotensin System


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Local Control of Organ Blood Flow

Matching of Organ Blood Flow to Organ

Metabolism

Matching of Organ Blood Flow to Blood

Oxygenation

Autoregulation of Organ Blood Flow

Fick Principle

Local Control Mechanisms


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Matching of Organ Blood Flow

to Organ Metabolism

Rate of Organ Metabolism (VO2)

OrganBlood Flow

Normal

Muscle Exercise


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Matching of Organ Blood Flow

to Blood Oxygenation

Arterial Blood Oxygenation

OrganBlood Flow

Normal

High Altitude or Pneumonia


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Autoregulation of Organ Blood Flow

ArterialPressure

(mmHg)

Organ

Blood Flow

Autoregulatory

Range

70 175

PResistance

Maximum

VasoconstrictionR = Rmax

Maximum

Vasodilation

R = Rmin

Critical

Closing Pressure

5


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Fick Principle

VO2 = Flow x {[O2]a[O2]v}

Rate of Metabolism Blood

Oxygenation

Regulated

VariableAverage Tissue [O2]

(Result of Regulation)

Local

Control


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Organ

Local Control Mechanisms

(Negative Feedback)

Organ

Metabolism

(VO2

)

Metabolite

(Vasodilator)

(-) Vasodilation

Artery

Pa

[O2]a

Arterioles Blood Flow

Vein


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Coronary and Cerebral Circulations

Coronary and cerebral circulations are

predominantly regulated by local control.

In case of cardiac output insufficiency (e.g.

hemorrhage), blood flow to coronary and

cerebral circulations is preserved while

blood flow to other organs is reduced.


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Endothelium-Derived Relaxing Factor

(NO, Nitric Oxide) Endothelial cells cover the wall of all blood

vessels

Mechanical rubbing (shear stress) and

receptor agonists (e.g. acetylcholine,

bradykinin) can elicit the release of NO

NO diffuses to vascular smooth musclecells to induce vasodilation


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Metabolism of Nitric Oxide

Endothelial

Cell

VascularSmooth Muscle

Cell

Blood Flow Shear Stress

Acetylcholine,

Bradykinin

[Ca2+]

Nitric Oxide Synthase

NO

Guanylate

CyclasecGMPBreakdown

Phosphodiesterase

Relaxation

NO


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Baroreceptor Reflex (Negative Feedback)

(+)

Vagus

(-)

Sympathetic Tone

HR HR, Contractility, TPR

(-)

Carotid and Aortic

BaroreceptorsSensor

Cardiovascular Center Controller/Comparator

Effectors

BP

RegulatedVariable


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Functional Significance of

Baroreceptor Reflex

Important in buffering sudden changes in

blood pressure in daily activities Not important in long-term regulation of

blood pressure


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Renin-Angiotensin System

BP Kidney Renin

Angiotensinogen

In plasmaAngiotensin I

Angiotensin II

ConvertingEnzyme (Lung)

VasoconstrictionFluid and Salt Retention

Blood Volume TPR

(-)


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Functional Significance of Renin-

Angiotensin System

Renin is produced by the kidney in response

to low BP Angiotensin II is an extremely potent

vasoconstrictor

Angiotensin Converting Enzyme (ACE) is apharmacologic target for controlling blood

pressure


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Required Reading

Chapters 17 and 18

Chapter 19, Section entitled The Renin-

Angiotensin System: its role in pressurecontrol and in hypertension.

autoregulation of the cardiovascular system

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