Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ch. 20 The Heart Describe the organization of the cardiovascular system. Discuss the differences between nodal cells and conducting cells and describe the components and functions of the conducting system of the heart. Identify the electrical events associated with a normal electrocardiogram. Explain the events of the cardiac cycle Define cardiac output, heart rate and stroke volume and describe the factors that influence these variables. Explain how adjustments in stroke volume and cardiac output are coordinated at different levels of activity.

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pulmonary circuit blood to and from the lungs System circuit blood to and from the rest of the body Vessels carry the blood through the circuits Arteries carry blood away from the heart Veins carry blood to the heart Capillaries permit exchange SECTION 20-1: Organization of the Cardiovascular System

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20.1 An Overview of the Cardiovascular System Figure 20.1

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Two classes of cardiac muscle cells 1) Specialized muscle cells of the conducting system 2) Contractile cells Cardiac Physiology SECTION 20-3: The Heartbeat

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The conducting system includes: Sinoatrial (SA) node Atrioventricular (AV) node Conducting cells Atrial conducting cells are found in internodal pathways Ventricular conducting cells consist of the AV bundle, bundle branches, and Purkinje fibers The Conducting System

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure The Conducting System of the Heart Figure 20.12

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Impulse Conduction through the Heart Figure 20.13

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings A recording of the electrical events occurring during the cardiac cycle The P wave accompanies the depolarization of the ventricles The QRS complex appears as the ventricles depolarize The T wave indicates ventricular repolarization The electrocardiogram (ECG)

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure An Electrocardiogram Figure 20.14a

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure An Electrocardiogram Figure 20.14b

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Resting membrane potential of approximately – 90mV Action potential Rapid depolarization A plateau phase unique to cardiac muscle Repolarization Refractory period follows the action potential Contractile Cells

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cardiac action potentials cause an increase in Ca 2+ around myofibrils Ca 2+ enters the cell membranes during the plateau phase Additional Ca 2+ is released from reserves in the sarcoplasmic reticulum Calcium Ion and Cardiac contraction

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure The Action Potential in Skeletal and Cardiac Muscle Figure 20.15

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure The Action Potential in Skeletal and Cardiac Muscle Figure 20.15

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The period between the start of one heartbeat and the beginning of the next During a cardiac cycle Each heart chamber goes through systole and diastole Correct pressure relationships are dependent on careful timing of contractions The cardiac cycle

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Phases of the Cardiac Cycle Figure 20.16

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Phases of the Cardiac Cycle Figure 20.16

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings atrial systole rising atrial pressure pushes blood into the ventricle atrial systole the end-diastolic volume (EDV) of blood is in the ventricles ventricular systole Isovolumetric contraction of the ventricles: ventricles are contracting but there is no blood flow Ventricular pressure increases forcing blood through the semilunar valves Pressure and volume changes

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pressure and volume changes: ventricular diastole The period of isovolumetric relaxation when all heart valves are closed Atrial pressure forces the AV valves open

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Pressure and Volume Relationships in the Cardiac Cycle Figure 20.17

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Auscultation – listening to heart sound via stethoscope Four heart sounds S 1 – “lubb” caused by the closing of the AV valves S 2 – “dupp” caused by the closing of the semilunar valves S 3 – a faint sound associated with blood flowing into the ventricles S 4 – another faint sound associated with atrial contraction Heart sounds

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Heart Sounds Figure 20.18a, b

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cardiac output – the amount of blood pumped by each ventricle in one minute Cardiac output equals heart rate times stroke volume Stroke Volume and Cardiac Output CO Cardiac output (ml/min) = HR Heart rate (beats/min) X SV Stroke volume (ml/beat) SECTION 20-4: Cardiodynamics

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure A Simple Model of Stroke Volume Figure 20.19a-d

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Autonomic innervation Cardiac reflexes Tone SA node Hormones Epinephrine (E), norepinephrine(NE), and thyroid hormone (T 3 ) Venous return Factors Affecting Heart Rate

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Factors Affecting Cardiac Output Figure 20.20

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Medulla Oblongata centers affect autonomic innervation Cardioacceleratory center activates sympathetic neurons Cardioinhibitory center controls parasympathetic neurons Receives input from higher centers, monitoring blood pressure and dissolved gas concentrations

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Autonomic Innervation of the Heart Figure 20.21

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Autonomic Innervation of the Heart Figure 20.21

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings SA node establishes baseline Modified by ANS Atrial reflex Basic heart rate established by pacemaker cells

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Pacemaker Function Figure 20.22

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Pacemaker Function Figure 20.22

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings EDV Frank-Starling principle ESV Preload Contractility Afterload Factors Affecting stoke volume

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Factors Affecting Stroke Volume Figure 20.23

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Factors Affecting Stroke Volume Figure 20.23

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sympathetic stimulation Positive inotropic effect Releases NE Parasympathetic stimulation Negative inotropic effect Releases ACh Autonomic Activity

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Heavy exercise can increase output by percent Trained athletes may increase cardiac output by 700 percent Cardiac reserve The difference between resting and maximal cardiac output Exercise and Cardiac Output

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Summary: Regulation of Heart Rate and Stroke Volume Sympathetic stimulation increases heart rate Parasympathetic stimulation decreases heart rate Circulating hormones, specifically E, NE, and T 3, accelerate heart rate Increased venous return increases heart rate EDV is determined by available filling time and rate of venous return ESV is determined by preload, degree of contractility, and afterload

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure A Summary of the Factors Affecting Cardiac Output Figure 20.24

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The goal of the cardiovascular system is to maintain adequate blood flow to all body tissues The heart works in conjunction with cardiovascular centers and peripheral blood vessels to achieve this goal SECTION 20-5: Heart & Cardiovascular System

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The organization of the cardiovascular system. The differences between nodal cells and conducting cells as well as the components and functions of the conducting system of the heart. The electrical events associated with a normal electrocardiogram. The events of the cardiac cycle Cardiac output, heart rate and stroke volume and the factors that influence these variables. How adjustments in stroke volume and cardiac output are coordinated at different levels of activity. You should now be familiar with: