last heart lecture 2010 - SA node Depolarization R...

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Figure 18.17 Atrial depolarization, initiated by the SA node, causes the P wave. P R T Q S SA node AV node With atrial depolarization complete, the impulse is delayed at the AV node. Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. P R T Q S P R T Q S Ventricular depolarization is complete. Ventricular repolarization begins at apex, causing the T wave. Ventricular repolarization is complete. P R T Q S P R T Q S P R T Q S Depolarization Repolarization 1 2 3 4 5 6
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4.2.8 Explain the events of each phase of the cardiac cycle 4.2.8.1 describe the pressure changes responsible for valve opening & closing & link these with resultant volume changes systole: contraction of heart; pumping OUT diastole: relaxation of heart; filling cardiac cycle: atrial systole + diastole ventricular systole + diastole Start = mid-to-late diastole: 1. Period of ventricular filling: mid-to-late diastole » pressure low (but P atria > P ventricles ), AV valves OPEN ; SL valves CLOSED after 70% ventricular filling, AV valves begin to close P wave & atrial systole ; atrial pressure increases & final 30% of blood enters ventricles ( end diastolic volume or EDV ) atrial diastole for rest of cycle J. Carnegie, UofO
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2. Ventricular systole (comprises QRS complex & T waves): ventricles begin to contract increased pressure closes AV valves - period of isovolumetric contraction (volume constant; a closed system) increased pressure opens SL valves ventricular ejection phase (aortic pressure up to 120 mm Hg) 3. Isovolumetric relaxation: early diastole ventricles relax; pressure decreases rapidly; backflow of aortic/pulmonary blood closes SL valves ( dicrotic notch ); ventricles a closed system = isovolumetric relaxation 4. Back to (1): atria continued in diastole & have been filling; when pressure > ventricular pressure, AV valves open and we are back to (1) J. Carnegie, UofO
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75 beat/min: each cardiac cycle=0.8 sec atrial systole = 0.1 sec ventricular systole = 0. 3 sec quiescent period = 0.4 sec 2 Features driving Cardiac Cycle: (a) Blood flow through heart controlled entirely by pressure changes (b) Blood flows from higher to lower pressure through any available opening ** electrical activity of left & right hearts is almost simultaneous
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1 2a 2b 3 Atrioventricular valves Aortic and pulmonary valves Open Open Closed Closed Closed Open Phase ESV Left atrium Right atrium Left ventricle Right ventricle Ventricular filling Atrial contraction Ventricular filling (mid-to-late diastole) Ventricular systole (atria in diastole) Isovolumetric contraction phase Ventricular ejection phase Early diastole Isovolumetric relaxation Ventricular filling 1 1 2a 2b 3 Electrocardiogram Left heart P 1st 2nd QRS P Heart sounds Atrial systole Dicrotic notch Left ventricle Left atrium EDV SV Aorta T Ventricular volume (ml) Pressure (mm Hg) 4.2.8.2 define these terms in relation to a cardiac cycle: systole, diastole, isovolumetric contraction & relaxation, dichrotic notch Figure 18.20
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4.2.8.3 indicate the physiological significance of the first and second heart sounds
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