BIOL 221 Lecture Notes - Lecture 2: Tachycardia, Bradycardia, Heart Valve
11 Feb 2020
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End-diastolic volume is the main controller of stroke volume. The blood stretches the myocardium before it contracts and so is known as preload. According to the frank-starling law of the heart the more the heart is stretched, the more strongly it contracts. Edv is related to filling time and venous return. Filling time is mainly related to how long the heart remains in diastasis. (recall that most of the blood entering the ventricles does so during the first few milliseconds after the av valves open. ) Venous return is the amount of blood that returns to the heart. Venous return depends on a number of factors that will be discussed later. Slow heart rate ___ time to fill. Fast heart rate ___ time to fill. Balanced by increased contractility (effect of epinephrine) except at very high rates. Filling time is determined by heart rate. A fast heart rate gives less time for the heart to fill.
