Cardiac Cycle Sequence of mechanical events that occurs during one heartbeat

Cardiac cycle sequence of mechanical events that

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Cardiac Cycle: Sequence of mechanical events that occurs during one heartbeat The two atria contract simultaneously A fraction of a second later, the two ventricles contract Contraction of chamber=systole, is followed by relaxation=diastole
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Cardiac Cycle: In diastole (relaxed), the atria continually receive blood from the veins-filling Blood builds up and the pressure increases, causing atrial systole (contraction), forcing the AV valves open=blood passes into ventricles
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Cardiac Cycle: The atria then relax and ventricular systole occurs, closing the AV valves and opening the semilunar valves Blood then pumps into the aorta and pulmonary artery As the ventricles empty and pressure drops=some backflow of blood occurs=closes the semilunar valves
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Heart Sounds : The events of the cardiac cycle create normal heart sounds Lubb-dubb First sound (lubb)=caused by closure of AV valves during ventricular systole Second sound (dubb)=from closure of the aortic and pulmonary semilunar valves “Wooshing” sound indicates murmur from incomplete valve closure Watch this video:
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Cardiac Output: Amount of blood ejected from the left ventricle in one minute Calculated by multiplying stroke volume x HR Stroke volume=amount of blood ejected by a ventricle in one contraction Depends upon contractility, pre-and- afterload Average=60-80 ml/beat, 5-6 ml/min
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Cardiac Output
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Cardiac Output and Exercise: During exercise, venous return increases and stretches the ventricular myocardium=causes it to contract more forcefully Referred to as Starlings Law of the Heart Stroke volume increases, more blood is pumped per beat, HR increases and thus cardiac output increases (up to 4 x and even more for athletes)
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Ejection Fraction: Measures how well the ventricle is functioning Measures how much blood is pumped by the left ventricle in one contraction Normal: 60% Lower values=ventricle not pumping sufficiently and that too much blood remains in ventricle Norm remaining values: 50-60 ml
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Preload and Afterload: Preload: how much blood is filling the ventricles Can be increased in hypervolemia Afterload: force at which the heart has to contract in order to eject blood Hypertension can increase afterload Narrowed valves can increase afterload
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Regulation of Heart Rate: Heart generates its own electrical impulse, beginning at the SA node But the nervous system can change the HR in response to environmental circumstances Either increase or decrease HR BP drop or decrease in O2 sat can increase HR
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Hormones and the Heart: Epinephrine: Secreted by adrenal medulla during stress increases HR and force of contraction=increases cardiac output and systolic BP Aldosterone: Produced by adrenal cortex Helps regulate blood levels of K and Na, both needed for electrical activity
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Hormones and the Heart: Atria secrete their own hormone=atrial natriuretic peptide Increases secretion of Na by kidneys
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