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PRINCIPLES OF HUMAN PHYSIOLOGY 13 THIRD EDITION Cindy L. Stanfield | William J. Germann The Cardiovascular System: Cardiac Function Part A PowerPoint® Lecture Slides prepared by W.H. Preston, College of the Sequoias Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Anatomy of the Heart • Four Chambers • Two atria • Two ventricles • Valves • Atrioventricular • Semilunar • Interventricular septum • Base • Apex Figure 13.1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Path of Blood Flow • Cardiovascular system = closed system • Flow through systemic and pulmonary circuits is in series • Left ventricle aorta systemic circuit vena cavae right atrium right ventricle pulmonary artery pulmonary circuit pulmonary veins left atrium left ventricle Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Path of Blood Flow Figure 13.2 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Heart Location Figure 13.5 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Ventricular Muscle Figure 13.6 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Properties of Cardiac Muscle • Cells are smaller than cells of skeletal muscle • Cells demonstrate branching • Striations are evident Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Properties of Cardiac Muscle • Intercalated disks • Gap junctions • Cause heart to contract as a unit • Desmosomes • Resist stress • Atria and ventricles • Copyright Separate units © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Properties of Cardiac Muscle • Aerobic muscle • No cell division after infancy—growth by hypertrophy • 99% contractile cells (for pumping) • 1% autorhythmic cells (set pace) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Function of Cardiac Muscle • Rhythmic contraction and relaxation generates heart pumping action • Contraction pushes blood out of heart into vasculature • Relaxation allows heart to fill with blood Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Heartbeat • Wave of contraction through cardiac muscle • Atria contract as a unit • Ventricles contract as a unit • Atrial contraction precedes ventricle contraction Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Valves and Unidirectional Blood Flow • Pressure within chambers of heart vary with heartbeat cycle • Pressure difference drives blood flow • High pressure to low pressure • Normal direction of flow • Atria to ventricles • Ventricles to arteries • Valves prevent backward flow of blood • All valves open passively based on pressure gradient Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Atrioventricular Valve Action Figure 13.7 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Semilunar Valve Action Figure 13.8 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Autorhythmic Cells Location SA Node AV Node Bundle of His Purkinje Fibers Firing Rate at Rest 70-80 APs/min* 40-60 APs/min 20-40 APs/min 20-40 APs/min • Cardiac cells are linked by gap junctions • Fastest depolarizing cells control other cells • Fastest cells = pacemaker = set rate for rest of heart * action potentials per minute Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Cardiac Electrical Connections Figure 13.9 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Conduction System of Heart Figure 13.10 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Pathway of Depolarization Figure 13.11 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Electrical Activity: Pacemaker Cell Figure 13.12 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Electrical Activity: Pacemaker Cell Table 13.1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Electrical Activity: Contractile Cell Figure 13.13 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Electrical Activity: Contractile Cell Table 13.2 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Cardiac Cycle Isovolumetric contraction Ventricular ejection Atrial contraction Isovolumetric relaxation Ventricular filling Ventricular filling Systole Left atrium Right atrium Right ventricle Early diastole Mid-to-late diastole Left ventricle Phase 1 2 3 4 1 Atrioventricular valves Open Closed Open Aortic and pulmonary (semilunar) valves Closed Open Closed Figure 13.18 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Ventricular Systole • Isovolumetric ventricular contraction • AV and aortic valves closed • Ventricular pressure increases until it exceeds atrial pressure • Ventricular ejection Copyright • Aortic valve opens • Blood moves from ventricle to aorta © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Ventricular Diastole • Isovolumetric ventricular relaxation • Ventricle muscle relaxes so that pressure is less than aorta • Aortic valve closes • Pressure in ventricle continues dropping until it is less than atrial pressure • Ventricular filling Copyright • AV valve opens • Blood moves from atria to ventricle • Passive until atrium contracts © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Ventricular Pressure Figure 13.19 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Aortic Pressure Figure 13.20 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Ventricular Volume Copyright • EDV = end-diastolic volume, volume of blood in ventricle at the end of diastole • ESV = end systolic volume, volume of blood in ventricle at the end of systole • SV = stroke volume, volume of blood ejected from ventricle each cycle. • SV = EDV -ESV © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 13.21 Stroke Volume Volume of blood ejected by the ventricle each beat Stroke volume = end diastolic volume – end systolic volume = 130 mL – 60 mL = 70 mL Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Ejection Fraction Fraction of end-diastolic volume ejected during a heartbeat Ejection fraction = stroke volume / end diastolic volume = 70 mL / 130 mL = 0.54 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Heart Sounds • Due to turbulent flow when valves close • First heart sound • Soft lubb • AV valves close simultaneously • Second heart sound Copyright • Louder dubb • Semilunar valves close simultaneously © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Heart Sounds Figure 13.22 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Cardiac Output Volume of blood pumped by each ventricle per minute • Cardiac output = CO = SV x HR • Average CO = 5 liters/min at rest • Average blood volume = 5.5 liters Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Regulation of Cardiac Output • Regulate heart rate and stroke volume • Extrinsic and intrinsic regulation Copyright • Extrinsic—neural and hormonal • Intrinsic—autoregulation © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Autonomic Inputs to Heart Figure 13.23 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Heart Rate - Determined by SA Node Firing Rate • SA node intrinsic firing rate = 100/min • No extrinsic control on heart, HR = 100 • SA node under control of ANS and hormones Copyright • Rest: parasympathetic dominates, HR = 75 • Excitement: sympathetic takes over, HR increases © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Effects of Sympathetic Activity on Heart Rate Increased sympathetic activity (nerves or epinephrine) Beta 1 receptors in SA node Increase open state of If and calcium channels Increase rate of spontaneous depolarization Increase heart rate Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Effects of Parasympathetic Activity on Heart Rate Increased parasympathetic activity (vagus nerve) Muscarinic Cholinergic Receptors in SA Node Increase open state of K channels and closed state of calcium channels Decrease rate of spontaneous depolarization and hyperpolarize cell Decrease heart rate Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Sympathetic Effects: SA Potentials Figure 13.25 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Factors Affecting Cardiac Output: Stroke Volume Primary factors affecting stroke volume • Ventricular contractility • End-diastolic volume • Afterload Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Stroke Volume • Ventricles never completely empty of blood • More forceful contraction will expel more blood • Extrinsic controls of SV • Sympathetic drive to ventricular muscle fibers • Hormonal control • Intrinsic controls of SV • Copyright Changes in EDV © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Extrinsic Control of Stroke Volume • Sympathetic innervation of contractile cells • Cardiac nerves • NE binds to 1 adrenergic receptors • Increases cardiac contractility • Parasympathetic innervation of contractile cells • Not significant • Hormones • Copyright Thyroid hormones, insulin and glucagon increase force of contraction © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Sympathetic Effects on Contractility • Increased sympathetic activity • Increased epinephrine release • Increases strength of contraction • Increases rate of contraction • Increases rate of relaxation Figure 13.27 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Principle of Frank-Starling’s Law • Increased EDV stretches muscle fibers • Fibers closer to optimum length • Optimum length = greater strength of contraction • Result = Increased SV Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Intrinsic Control - Frank-Starling’s Law Increase venous return Increase strength of contraction Increase stroke volume Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Starling’s Law Figure 13.28 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Starling’s Law Figure 13.29 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Factors Affecting End-Diastolic Volume • End-diastolic pressure = preload • Filling time • Atrial pressure • Central venous pressure • Afterload = pressure in aorta during ejection Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Factors Influencing Stroke Volume Venous return Sympathetic activity or Epinephrine Ventricle End-diastolic volume Contractility Arterial pressure (afterload) Stroke volume Figure 13.30 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Factors Influencing Stroke Volume Venous return Ventricle End-diastolic volume Stroke volume Figure 13.30, step 1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Factors Influencing Stroke Volume Venous return Sympathetic activity or Epinephrine Ventricle End-diastolic volume Contractility Stroke volume Figure 13.30, step 2 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Factors Influencing Stroke Volume Venous return Sympathetic activity or Epinephrine Ventricle End-diastolic volume Contractility Arterial pressure (afterload) Stroke volume Figure 13.30, step 3 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Regulation of Cardiac Output Figure 13.31 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.