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Cardiac Output – amount of blood pumped from the ventricles in one minute

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.

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Cardiac Output – amount of blood pumped from the ventricles in one minute

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  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 • 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) • Contractility – contractile strength achieved at given muscle length • --extrinsic factor • --calcium = more cross bridging between myosin and actin • --sympathetic stimulation

  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 • Hormones • -- epinephrine > enhances heart rate and contractility • --Thyroid Hormone >enhances epinephrine and norepinephrine effects • >alone provides slower, sustained increase in heart rate • 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 • 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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