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UNCG KIN 292 - The Cardiac Cycle

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KIN 292 1nd Edition Lecture 23 Outline of Last Lecture I. 13.1- overview of the cardiovascular system, II. 13.2- pathway of blood flow through the heart, III. 13.3- anatomy of the heart IV. 13.4- electrical activity of the heartOutline of Current Lecture I. 13.4 Electrical Activity of the Heart - continuedII. 13.5 The Cardiac CycleCurrent Lecture13.5 Cardiac cycle- Events associated with the flow of blood through the heart during a single complete heartbeat- Two main periods of cardiac cycle- Systole: ventricle contraction- Diastole: ventricle relaxation- Valves open passively due to pressure gradients- AV valves open when atrial pressure > ventricular pressure- Semilunar valves (aortic and pulmonary) open when ventricular pressure > arterial pressure- Know:o Phases of the cardiac cycleo Atrial and ventricular pressureo Aortic pressureo Ventricular volumeo Heart soundso ECG/EKG – from labPhase OneThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Ventricular fillingo Middle of ventricular diastoleo Venous returno AV valve openso Blood moves from atria to ventricleo Pulmonary and aortic valves are closedo Passive until atrium contractsPhase Two- Isovolumetric ventricular contractiono Start of systoleo Ventricle contracts—increases pressureo AV and semilunar valves closedo No blood entering or exiting ventriclePhase Three• Ventricular ejection• Remainder of systole• Pressure in ventricles > pressure in arteries • Semilunar valves open• Ventricular pressure < aortic pressure• Semilunar valves closePhase Four• Isovolumetric ventricular relaxation Onset of diastole Ventricle relaxes—decreases pressure AV and semilunar valves closed No blood entering or exiting ventricleAtrial and Ventricular Pressure • Phase 1• Atrial pressure rises slowly with filling of blood• Ventricular pressure is low• Small rise in VP at end due to atrial contraction• Phase 2• Rapid rise in ventricular pressure• Atrial pressure falls• Phase 3• Ventricular pressure falls• Atrial pressure falls further until late systoleAortic Pressure• Diastole• Starts when Aortic valve closes• Backflow of blood in aorta causes slight increase—dicrotic notch• Blood is still leaving aorta, so pressure falls• Lowest point = diastolic pressure• Systole• Aortic valve opens• Pressure rises rapidly with ejection• Highest point = systolic pressure• Aortic valve closes• Pulsatile flow from heart to large arteries is converted to continuous flow by artery properties • Aorta (and large arteries)—elastic• Pressure reservoir• Stores energy during systole as walls expand• Releases energy during diastole as walls recoil inward• Aortic pressure maintains blood flow through the entire cardiac cycle• Ejection fraction (EF): fraction of end-diastolic volume ejected during a heartbeatEF = stroke volume/end diastolic volumeEF = 70 mL/130 mL = 0.54(i.e., 54% at rest)• First heart sound• Soft "lubb“ --AV valves close simultaneously at isovolumetric contraction• Second heart sound• Louder "dupp“ -- Semilunar valves close simultaneously at isovolumetric


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UNCG KIN 292 - The Cardiac Cycle

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