Chapter 017

The Human Body in Health and

Illness,

4th edition

Barbara Herlihy

Chapter 17:

Function of the Heart

Lesson 17-1 Objectives

• Define cardiac cycle with respect to systole and diastole.

• Describe the autonomic innervation of the heart.

• Define cardiac output and explain how changes in heart rate and/or stroke volume change cardiac output.

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights

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Lesson 17-1 Objectives (cont’d.)

• Describe the effect of Starling’s law of the heart on myocardial contraction.

• Define preload and explain how it affects cardiac output.

• Define afterload and identify the major factors that determine afterload.


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Lesson 17-1 Objectives (cont’d.)

• Describe the inotropic effect on myocardial contraction.

• Define the special clinical vocabulary used to describe cardiac function.

• Define heart failure and differentiate between right-sided and left-sided heart failure.


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Cardiac Cycle: One Heartbeat

• Systole (contraction) and diastole (relaxation) act in coordination.


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Autonomic Control of the Heart

• Allows heart to respond to changing body needs

• Involves sympathetic and parasympathetic (vagal) nerves


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Autonomic Wiring

• Sympathetics– SA node– AV node– Ventricular

myocardium

• Parasympathetics– SA node– AV node


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Autonomic Neurotransmitters

• Sympathetics– Adrenergics– Norepinephrine (NE)

• Parasympathetics– Cholinergic– Acetylcholine (ACh)


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Firing of the Sympathetic System

↑SA node activity and heart rate

↑Speed of cardiac impulse through conduction system

↑Force of myocardial contraction


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Firing of the Parasympathetic System

↓SA node activity and heart rate

↓Speed of cardiac impulse from SA to AV node

• No effect on strength of contraction


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Cardiac Output (CO)

• CO is amount of blood pumped by each ventricle in 1 minute (mL/min).

• CO = heart rate × stroke volume• CO in the healthy heart can increase four to

five times; called the cardiac reserve


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Heart Rate and Stroke Volume

• Heart rate: Number of times the heart beats each minute caused by SA node’s firing

• Stroke volume: Amount of blood pumped by the ventricle per beat

• CO can be altered by changing heart rate and/or stroke volume


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How to Change Stroke Volume • Starling’s law of the heart

– Changes the force of contraction by stretching the myocardium

– Mechanism: Aligns the sarcomeres for greater interaction between actin and myosin

• Inotropic effect – Changes the force of contraction without

stretching the myocardium– Mechanism: Makes calcium more available to the

contractile proteinsCopyright © 2011, 2007 by Saunders,

an imprint of Elsevier Inc. All rights reserved.

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How to Change Stroke VolumeStarling’s law of the heart: What goes in, comes out


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Stroke Volume: Ejection Fraction

• Ejection fraction is the percentage of blood volume in the ventricle that is pumped by the heart.

• Normal ejection fraction is about 67%.• Exercise can increase ejection fraction.• Heart failure decreases ejection fraction.


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Heart Talk: Clinical Terms

• Preload: EDV– Amount of blood in

ventricle at the end of diastole (EDV)

– Basis of Starling’s law of the heart

• Afterload: Resistance– Caused by blood

pressure Copyright © 2011, 2007 by Saunders,


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Heart Talk: Clinical Terms (cont’d.)

• Inotropic effect: Change in myocardial contraction not caused by stretch

• Chronotropic effect: Change in heart rate• Dromotropic effect: Change in the speed at

which the cardiac impulse travels from the SA node through the AV node and His-Purkinje system


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Heart Talk: Beta1-Adrenergic Receptors

• Locations SA node AV node Myocardium

• Activated by NE

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 18

Effects of Beta1-Adrenergic Receptors

Effect of Activating(+) Chronotropic(+) Dromotropic (+) Inotropic

Effect of Blocking() Chronotropic() Dromotropic () Inotropic


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Heart Talk: Muscarinic Receptors

• Locations SA node AV node

• Activated by ACh


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Effects of Muscarinic Receptors

Effects of Activating() Chronotropic () Dromotropic

Effects of Blocking(+) Chronotropic (+) Dromotropic


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Heart Failure: Left-Sided• Backward

– Poor left ventricular function

– Fluid backs up into lungs

• Forward– Poor left ventricular

function– Decreases blood flow

to systemic circulationCopyright © 2011, 2007 by Saunders,


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Heart Failure: Right-Sided

• Backward– Blood backs up into

veins that drain blood to the right heart


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Heart Failure: Treatment Goals

• Strengthen myocardial contractile force• Remove excess water• Decrease work of the heart• Protect the heart from excess sympathetic

nerve activity


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Health & Medicine

Chapter 017