BIOL 1119 Lecture Notes - Lecture 13: Hypocalcaemia, Arteriole, Vasodilation
19 Aug 2016
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Governed by three factors: preload, contractility, afterload. Preload: amount of tension in ventricular myocardium before it contracts. Moderate stretch enables myocytes to generate more tension during contraction. The more a muscle is stretched, the better the overlap between filaments and the stronger the contraction. Frank-starling law of heart: sv edv ventricles eject as much blood as they receive. More they are stretched, the stronger the contraction. The parasympathetic system via the vagus nerve has no significant effect on strength of ventricular contraction because it does not innervate the myocardium. Pressure in arteries above semilunar valves opposes opening of valves. Increase afterload, decrease sv any restricting of arterial circulation increases afterload (lung disease, atherosclerosis, etc. ) Continuous increases in afterload causes hypertrophy of ventricular myocardium, may lead to weakening and failing of ventricles (see lecture 11 for notes above) Contractility is contraction force or how hard the myocardium contracts for a given preload. Contractility is not caused by stretch of cardiac muscle.
