TEACH Lesson Plan Manual for Herlihy s The Human Body in Health and Illness 5 th edition

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1 TEACH Lesson Plan Manual for Herlihy s The Human Body in Health and Illness 5 th edition Chapter 17 Function of the Heart

2 Lesson 17.1 Function of the Heart 1. Define cardiac cycle with respect to systole and diastole. 2. Describe the autonomic innervation of the heart, including: Define cardiac output. Describe the effect of Starling's law of the heart on myocardial contraction. Describe the inotropic effect on myocardial contraction. Explain how changes in heart rate and/or stroke volume change cardiac output. 2

3 Lesson 17.1 Function of the Heart, cont d 3. Define specific clinical vocabulary used to describe cardiac function, including: Define preload (end diastolic volume) and explain how it affects cardiac output. Define afterload and identify the major factors that determine afterload. 4. Define heart failure and differentiate between right-sided and left-sided heart failure. 3

4 Cardiac Cycle: One Heartbeat Systole (contraction) and diastole (relaxation) act in coordination 4

5 Autonomic Control of the Heart Allows heart to respond to changing body needs Involves sympathetic and parasympathetic (vagal) nerves 5

6 Autonomic Wiring Sympathetics Sinoatrial (SA) node Atrioventricular (AV) node Ventricular myocardium Parasympathetics SA node AV node 6

7 Firing of the Sympathetic System Increases SA node activity and heart rate Increases speed of cardiac impulse through conduction system Increases force of myocardial contraction 7

8 Firing of the Parasympathetic System Decreases SA node activity and heart rate Decreases speed of cardiac impulse from SA to AV node No effect on strength of contraction 8

9 Cardiac Output Cardiac output (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 9

10 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 10

11 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 proteins 11

12 How to Change Stroke Volume, cont d Starling s law of the heart: What goes in, comes out 12

13 Changing Cardiac Output CO can be increased four to five times the resting output Capacity to increase output above resting rate = cardiac reserve 13

14 Clinical Terms: End-Diastolic Volume and Preload End-diastolic volume Amount of blood in ventricle at resting phase's end Preload Another name for end-diastolic volume 14

15 Clinical Terms: 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 15

16 Clinical Terms: Afterload Afterload: Resistance Caused by blood pressure 16

17 More Clinical Terms 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 17

18 Heart Talk: Receptor Language Locations SA node AV node Myocardium Activated by norepinephrine 18

19 Effects of Beta 1 -Adrenergic Receptors Effect of activating (+) Chronotropic (+) Dromotropic (+) Inotropic Effect of blocking ( ) Chronotropic ( ) Dromotropic ( ) Inotropic 19

20 Heart Talk: Muscarinic Receptors Locations SA node AV node Activated by acetylcholine (ACh) 20

21 Effects of Muscarinic Receptors, cont d Effects of activating ( ) Chronotropic ( ) Dromotropic Effects of blocking (+) Chronotropic (+) Dromotropic 21

22 Heart Failure: Left-Sided Backward Poor left ventricular function Fluid backs up into lungs Forward Poor left ventricular function Decreases blood flow to systemic circulation 22

23 Heart Failure: Right-Sided Backward Blood backs up into veins that drain blood to the right heart 23

24 Heart Failure: Treatment Goals Strengthen myocardial contractile force Remove excess water Decrease work of the heart Protect the heart from excess sympathetic nerve activity 24

25 Questions? 25

Electrical Conduction

Sinoatrial (SA) node Electrical Conduction Sets the pace of the heartbeat at 70 bpm AV node (50 bpm) and Purkinje fibers (25 40 bpm) can act as pacemakers under some conditions Internodal pathway from