2 Contractile Cells Resting membrane potential of approximately –90mV Action potentialRapid depolarizationA plateau phase unique to cardiac muscleRepolarizationRefractory period follows the action potential
3 Calcium Ion and Cardiac contraction Cardiac action potentials cause an increase in Ca2+ around myofibrilsCa2+ enters the cell membranes during the plateau phaseAdditional Ca2+ is released from reserves in the sarcoplasmic reticulum
4 Figure 20.15 The Action Potential in Skeletal and Cardiac Muscle
5 Figure 20.15 The Action Potential in Skeletal and Cardiac Muscle
6 The cardiac cycleThe period between the start of one heartbeat and the beginning of the nextDuring a cardiac cycleEach heart chamber goes through systole and diastoleCorrect pressure relationships are dependent on careful timing of contractionsPLAYAnimation: Intrinsic Conduction System
9 Pressure and volume changes: atrial systole rising atrial pressure pushes blood into the ventricleatrial systolethe end-diastolic volume (EDV) of blood is in the ventricles
10 Pressure and volume changes: ventricular systole Isovolumetric contraction of the ventricles: ventricles are contracting but there is no blood flowVentricular pressure increases forcing blood through the semilunar valves
11 Pressure and volume changes: ventricular diastole The period of isovolumetric relaxation when all heart valves are closedAtrial pressure forces the AV valves open
12 Figure 20.17 Pressure and Volume Relationships in the Cardiac Cycle
13 Heart sounds Auscultation – listening to heart sound via stethoscope Four heart soundsS1 – “lubb” caused by the closing of the AV valvesS2 – “dupp” caused by the closing of the semilunar valvesS3 – a faint sound associated with blood flowing into the ventriclesS4 – another faint sound associated with atrial contraction
16 Stroke Volume and Cardiac Output Cardiac output – the amount of blood pumped by each ventricle in one minuteCardiac output equals heart rate times stroke volumeCOCardiac output(ml/min)=HRHeart rate(beats/min)XSVStroke volume(ml/beat)
17 Figure 20.19 A Simple Model of Stroke Volume Figure 20.19a-d
30 Exercise and Cardiac Output Heavy exercise can increase output by percentTrained athletes may increase cardiac output by 700 percentCardiac reserveThe difference between resting and maximal cardiac outputPLAYAnimation: Cardiac cycle
31 Summary: Regulation of Heart Rate and Stroke Volume Sympathetic stimulation increases heart rateParasympathetic stimulation decreases heart rateCirculating hormones, specifically E, NE, and T3, accelerate heart rateIncreased venous return increases heart rateEDV is determined by available filling time and rate of venous returnESV is determined by preload, degree of contractility, and afterload
32 Figure 20.24 A Summary of the Factors Affecting Cardiac Output
33 SECTION 20-5 The Heart and the Cardiovascular System
34 The heart is part of the cardiovascular system The goal of the cardiovascular system is to maintain adequate blood flow to all body tissuesThe heart works in conjunction with cardiovascular centers and peripheral blood vessels to achieve this goal
35 You should now be familiar with: The organization of the cardiovascular system.The location and general features of the heart, including the pericardium.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.
36 You should now be familiar with: The events of the cardiac cycle including atrial and ventricular systole and diastole, and the heart sounds related to specific events in the 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.
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