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Cardiac Output – amount of blood pumped from the ventricles in one minute Stroke Volume – amount of blood pumped from the heart in one ventricular contraction.

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Presentation on theme: "Cardiac Output – amount of blood pumped from the ventricles in one minute Stroke Volume – amount of blood pumped from the heart in one ventricular contraction."— Presentation transcript:

1 Cardiac Output – amount of blood pumped from the ventricles in one minute Stroke Volume – amount of blood pumped from the heart in one ventricular contraction SV = EDV-ESV End Diastolic Volume (EDV) – amount of blood in the ventricles at the end of diastole/ before contraction End Systolic Volume (ESV) – amount of blood in the ventricles at the end of systole/ after contraction

2 3 Factors That Influence Stroke Volume 1)Preload – degree to which cardiac muscle cells are stretched just before contraction (Frank-Starling Law of the Heart) --intrinsic factor --determined by EDV --most important factor influencing EDV is venous return (slow heart rate, venoconstriction) 2)Contractility – contractile strength achieved at given muscle length --extrinsic factor --calcium = more cross bridging between myosin and actin --sympathetic stimulation

3 3)Afterload -- back pressure of arterial blood that must be overcome for ventricules to eject blood --extrinsic factor

4 Regulation of Heart Rate Autonoic Nervous System Sympathetic >causes SA node to fire more rapidly because threshold is reached more quickly Parasympathetic >slows heart rate because acetylcholine hyperpolarizes the heart

5 Chemical Regulation 1)Hormones -- epinephrine > enhances heart rate and contractility --Thyroid Hormone >enhances epinephrine and norepinephrine effects >alone provides slower, sustained increase in heart rate 2)Ions --Ca 2+ deficiency in blood depresses heart -- K + -- excessive lowers resting potential (makes it more positive) --deficiency cause heart to beat weakly and out of rhythm

6 Irregular Heart Rates 1)Tachycardia – abnormally fast heart rate -- more than 100 bpm Causes – stress, certain drugs, heart disease 2) Bradycardia – slow heart rate -- slower than 60 bpm Causes – certain drugs, parasympathetic nervous activation, endurance training


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