PHSL232 Lecture Notes - Lecture 4: Tachycardia, Stroke Volume, Cardiac Muscle Cell

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31 Jul 2013
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Intrinsic control of cardiac function by heart rate (treppe effect) Intrinsic control of cardiac function by frank-starling mechanism. Controls originating from within the heart: intrinsic. Stroke volume (dictated by preload, afterload, contractility) Both of these operate continuously to adjust the heart and vessels to maintain map. Overall intrinsic control of heart rate seems very limited. Extrinsic parasympathetic and sympathetic nervous system control seems to be much more important. Treppe effect: bowditch effect: positive pressure/force-frequency relationship: myocardial contraction increases with frequency. Mechanism: increase in ca per unit time (increase in na due to slower na/k pump). Negative force/frequency relationship is the hallmark of heart failure. Determined by pre-load (input), afterload (resistance to output), and contractility (force produced). Increase in preload produces a larger stroke volume: starling"s law of the heart" or the frank-starling mechanism". Increase in venous return = ventricle is filled more = increased pre-load.

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