Cardiac Output: Heart Rate X Stroke Volume

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Chapter 14, part BCardiovascular Physiology

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Autorhythmic Cells: Initiation of SignalsPacemaker membrane potential I-f channels Na+ influx Ca++ channels – influx, to AP Slow K+ open – repolarizationPLAYAnimation: Cardiovascular System: Cardiac Action Potential

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Autorhythmic Cells: Initiation of SignalsFigure 14-16: Action potentials in cardiac autorhythmic cells

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Sympathetic and ParasympatheticSympathetic – speeds heart rate by  Ca++ & I-f channel flow Parasympathetic – slows rate by  K+ efflux &  Ca++ influxFigure 14-17: Modulation of heart rate by the nervous system

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Coordinating the Pump: Electrical Signal FlowAP from autorhythmic cells in sinoatrial node (SA) Spreads via gap junctions down internodal pathways and across atrial myocardial cells (atrial contraction starts) Pause – atrioventricular (AV) node delay AV node to bundles of His, branches & Perkinje fibers Right and left ventricular contraction from apex upword

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Coordinating the Pump: Electrical Signal FlowFigure 14-18: Electrical conduction in myocardial cells

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Coordinating the Pump: Electrical Signal FlowPLAYAnimation: Cardiovascular System: Intrinsic Conduction SystemFigure 14-19a: Electrical conduction in the heart

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Electrocardiogram (ECG): Electrical Activity of the HeartEinthoven's triangle P-Wave – atria QRS- wave – ventricles T-wave – repolarizationFigure 14-20: Einthoven’s triangle

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Electrocardiogram (ECG): Electrical Activity of the HeartFigure 14-21: The electrocardiogram

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ECG Information Gained(Non-invasive) Heart Rate Signal conduction Heart tissue ConditionsFigure 14-24: Normal and abnormal electrocardiograms

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Heart Cycle: Heart Chambers and the Beat SequencePLAYAnimation: Cardiovascular System: The Cardiac Cycle1. Late diastole: all chambers relax, filling with blood 2. Atrial systole: atria contract, add 20% more blood to ventricles 3. Isovolumic ventricular contraction: closes AV valves ("lub"), builds pressure

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Heart Cycle: Finish and Around To the Start4. Ventricular ejection: pushes open semi lunar valves, blood forced out 5. Ventricular relaxation: aortic back flow slams semi lunar valves shut ("dup") AV valves open refilling starts – back to start of cycle

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Heart CycleFigure 14-25: Mechanical events of the cardiac cycle

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Summary of Heart Beat: Electrical, Pressure and Chamber VolumesFigure 14-27: The Wiggers diagram

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Regulators of the Heart: Reflex Controls of RateRange: about 50 – near 200 Typical resting: near 70 AP conduction Muscle Contraction Parasympathetic slows Sympathetic speeds

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Regulators of the Heart: Reflex Controls of RateFigure 14-28: Reflex control of heart rate

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Cardiac Output: Heart Rate X Stroke VolumeAround 5L : (72 beats/m  70 ml/beat = 5040 ml) Rate: beats per minute Volume: ml per beat EDV - ESV Residual (about 50%)PLAYAnimation: Cardiovascular System: Cardiac Output

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Cardiac Output: Heart Rate X Stroke VolumeFigure 14-26: The Wiggers diagram

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Regulators of the Heart: Factors Influencing Stroke VolumeStarlings Law – stretch Force of contraction Venous return: Skeletal pumping Respiratory pumping

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Regulators of the Heart: Factors Influencing Stroke VolumeFigure 14-29: Length-force relationships in the intact heart

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Regulators of the Heart: Factors Influencing Stroke VolumeFigure 14-31: Factors that affect cardiac output

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SummaryAnatomy and physiology of the Heart , its chambers, muscles, valves, and its pacemaker Mechanism of cardiac muscle stimulation and contraction Blood vessels and fluid flow down a pressure gradient Electrical control of the beat sequence, and ECG information Influence of beat rate and stroke volume by ANS and hormones

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Last Updated: 8th March 2018

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