PHGY 210 Chapter Notes - Chapter 12.5-12.6: Aortic Valve, Heart Valve, Endoplasmic Reticulum
18 Mar 2017
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Na/ca countertransporters --ends contraction: strength of muscle contraction dependent on [ca] in cytosol, resting heartbeat release of calcium not enough to saturate all troponin sites. Refractory period: cardiac muscle unable undergo summation due to long absolute refractory period, lasts almost as long as contraction (250ms) so muscle can"t be re-excited when contracted, results from inactivation of sodium channels, making membrane unexcitable. Increases sensitivity of troponin to calcium, increases ca release from sarcoplasmic reti: overall, increase in venous return (flow blood from veins to heart) = increase end- diastolic volume = increase stroke volume = increase cardiac output. If one side of heart pumps more blood than the other, increase output of other side to ensure blood does not accumulate. Sympathetic regulation: norepinephrine is neurotransmitter than increases ventricular contractility -- strength contraction at any given end-diastolic volume, different from change in force from frank-starling mechanism.
