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The Cardiac Cycle Heart Murmur
Sounds produced by regurgitation through valves
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The Cardiac Cycle Figure 18–18 Heart Sounds
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Cardiodynamics The movement and force generated by cardiac contractions End-diastolic volume (EDV) End-systolic volume (ESV) Stroke volume (SV) SV = EDV – ESV Ejection fraction The percentage of EDV represented by SV Cardiac output (CO) The volume pumped by left ventricle in 1 minute
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Cardiodynamics Figure 18–19 A Simple Model of Stroke Volume
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Cardiodynamics Cardiac Output CO = HR X SV
CO = cardiac output (mL/min) HR = heart rate (beats/min) SV = stroke volume (mL/beat)
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Cardiodynamics Factors Affecting Cardiac Output Cardiac output
Adjusted by changes in heart rate or stroke volume Heart rate Adjusted by autonomic nervous system or hormones Stroke volume Adjusted by changing EDV or ESV
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Cardiodynamics Figure 18–20 Factors Affecting Cardiac Output
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Cardiodynamics Factors Affecting the Heart Rate Autonomic innervation
Cardiac plexuses: innervate heart Vagus nerves (X): carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus Cardiac centers of medulla oblongata: cardioacceleratory center controls sympathetic neurons (increases heart rate) cardioinhibitory center controls parasympathetic neurons (slows heart rate)
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Cardiodynamics Autonomic Innervation Cardiac reflexes
Cardiac centers monitor: blood pressure (baroreceptors) arterial oxygen and carbon dioxide levels (chemoreceptors) Cardiac centers adjust cardiac activity Autonomic tone Dual innervation maintains resting tone by releasing ACh and NE Fine adjustments meet needs of other systems
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Cardiodynamics Figure 18–21 Autonomic Innervation of the Heart
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Cardiodynamics Effects on the SA Node
Sympathetic and parasympathetic stimulation Greatest at SA node (heart rate) Membrane potential of pacemaker cells Lower than other cardiac cells Rate of spontaneous depolarization depends on Resting membrane potential Rate of depolarization ACh (parasympathetic stimulation) Slows the heart NE (sympathetic stimulation) Speeds the heart
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Cardiodynamics Figure 18–22 Autonomic Regulation of Pacemaker Function
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Cardiodynamics Atrial Reflex Also called Bainbridge reflex
Adjusts heart rate in response to venous return Stretch receptors in right atrium Trigger increase in heart rate Through increased sympathetic activity
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Cardiodynamics Hormonal Effects on Heart Rate
Increase heart rate (by sympathetic stimulation of SA node) Epinephrine (E) Norepinephrine (NE) Thyroid hormone
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Cardiodynamics Factors Affecting the Stroke Volume
The EDV: amount of blood a ventricle contains at the end of diastole Filling time: duration of ventricular diastole Venous return: rate of blood flow during ventricular diastole
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Cardiodynamics Preload
The degree of ventricular stretching during ventricular diastole Directly proportional to EDV Affects ability of muscle cells to produce tension
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The Conducting System Figure 18–13 Impulse Conduction through the Heart
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The Conducting System Figure 18–13 Impulse Conduction through the Heart
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The Conducting System The AV Bundle In the septum
Carries impulse to left and right bundle branches Which conduct to Purkinje fibers (Step 4) And to the moderator band Which conducts to papillary muscles
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The Conducting System Figure 18–13 Impulse Conduction through the Heart
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The Conducting System Purkinje Fibers
Distribute impulse through ventricles (Step 5) Atrial contraction is completed Ventricular contraction begins
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The Conducting System Figure 18–13 Impulse Conduction through the Heart
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The Conducting System Abnormal Pacemaker Function
Bradycardia: abnormally slow heart rate Tachycardia: abnormally fast heart rate Ectopic pacemaker Abnormal cells Generate high rate of action potentials Bypass conducting system Disrupt ventricular contractions
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The Conducting System Electrocardiogram (ECG or EKG)
A recording of electrical events in the heart Obtained by electrodes at specific body locations Abnormal patterns diagnose damage
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The Conducting System Features of an ECG P wave QRS complex T wave
Atria depolarize QRS complex Ventricles depolarize T wave Ventricles repolarize
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The Conducting System Time Intervals Between ECG Waves P–R interval
From start of atrial depolarization To start of QRS complex Q–T interval From ventricular depolarization To ventricular repolarization
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The Conducting System Figure 18–14a An Electrocardiogram: Electrode Placement for Recording a Standard ECG
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The Conducting System Figure 18–14b An Electrocardiogram: An ECG Printout
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The Conducting System Contractile Cells
Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart Resting Potential Of a ventricular cell: about –90 mV Of an atrial cell: about –80 mV
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The Conducting System Figure 18–15 The Action Potential in Skeletal and Cardiac Muscle
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The Conducting System Figure 18–15 The Action Potential in Skeletal and Cardiac Muscle
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The Conducting System Refractory Period Absolute refractory period
Long Cardiac muscle cells cannot respond Relative refractory period Short Response depends on degree of stimulus
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The Conducting System Timing of Refractory Periods
Length of cardiac action potential in ventricular cell 250–300 msecs: 30 times longer than skeletal muscle fiber long refractory period prevents summation and tetany
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The Conducting System The Role of Calcium Ions in Cardiac Contractions
Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils
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The Conducting System The Role of Calcium Ions in Cardiac Contractions
20% of calcium ions required for a contraction Calcium ions enter plasma membrane during plateau phase Arrival of extracellular Ca2+ Triggers release of calcium ion reserves from sarcoplasmic reticulum
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The Conducting System The Role of Calcium Ions in Cardiac Contractions
As slow calcium channels close Intracellular Ca2+ is absorbed by the SR Or pumped out of cell Cardiac muscle tissue Very sensitive to extracellular Ca2+ concentrations
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The Conducting System The Energy for Cardiac Contractions
Aerobic energy of heart From mitochondrial breakdown of fatty acids and glucose Oxygen from circulating hemoglobin Cardiac muscles store oxygen in myoglobin
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