BIOL 1119 Lecture Notes - Lecture 13: Hypercalcaemia, Vasomotor Center, Hypocalcaemia
16 Feb 2017
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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. Relaxed cardiocyte is under stretched shorter than optimal length. Relaxed cardiac muscle is not at optimal length unlike relaxed skeletal muscle. Frank starling law of heart sv edv: ventricles eject as much blood as they receive. More they are stretched, stronger the contraction. Greater filling causes additional stretching of cardiac muscle = Contractility: contraction force for a given preload increase force. Sympathetic nervous system and chemicals affect contractility. Parasympathetic system via the vagus nerve has no significant effect on strength of ventricular contraction because it does not innervate the myocardium parasymp only hr. Afterload: pressure in arteries about semilunar valve opposes opening of valves.
