white_o
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Can someone help me understand Starling's Law of the Heart please?

I'm particularly stuck on the significance of stretching sarcomeres to optimal length, the left ventricular filling pressure and the 'all or nothing' idea...

Thanks!
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AortaStudyMore
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(Original post by white_o)
Can someone help me understand Starling's Law of the Heart please?

I'm particularly stuck on the significance of stretching sarcomeres to optimal length, the left ventricular filling pressure and the 'all or nothing' idea...

Thanks!
This is basically the law saying that the more you stretch a muscle the more powerful it will contract. There's a couple of theories why this happens, the first one states that in an unstretched muscle the actin filaments are overlapping in the sarcomere and so there are less actin-myosin binding sites available, if you stretch the muscle then you expose more binding sites and the muscle will contract with more force. There obviously becomes a point where you stretch it too far and then the force of contraction decreases again, but this isn't a problem in the heart because it is surrounded by a sac called the pericardium that stops it stretching too much. The second theory is something to do with calcium, and that the more you stretch a muscle the more powerful the contraction is for a given amount of calcium (remember that calcium is needed to stimulate muscle contraction). I can't remember the details of this, I'm sure someone else will. As for the all or nothing principal, I think that means that the size of the action potential reaching a muscle fibre doesn't determine the strength of the fibre contraction. The strength by which a muscle contracts depends on the frequency of impulses reaching the muscle as well as the type of muscle stimulated (fast twitch etc). And finally, the left ventricular filling is known as the "preload", this is the initial stretching force on the muscle that primes the muscle for a powerful contraction.
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white_o
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(Original post by AortaStudyMore)
This is basically the law saying that the more you stretch a muscle the more powerful it will contract. There's a couple of theories why this happens, the first one states that in an unstretched muscle the actin filaments are overlapping in the sarcomere and so there are less actin-myosin binding sites available, if you stretch the muscle then you expose more binding sites and the muscle will contract with more force. There obviously becomes a point where you stretch it too far and then the force of contraction decreases again, but this isn't a problem in the heart because it is surrounded by a sac called the pericardium that stops it stretching too much. The second theory is something to do with calcium, and that the more you stretch a muscle the more powerful the contraction is for a given amount of calcium (remember that calcium is needed to stimulate muscle contraction). I can't remember the details of this, I'm sure someone else will. As for the all or nothing principal, I think that means that the size of the action potential reaching a muscle fibre doesn't determine the strength of the fibre contraction. The strength by which a muscle contracts depends on the frequency of impulses reaching the muscle as well as the type of muscle stimulated (fast twitch etc). And finally, the left ventricular filling is known as the "preload", this is the initial stretching force on the muscle that primes the muscle for a powerful contraction.
Thanks very much!
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