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sympathetic stimulation

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sympathetic stimulation

Postby bionewbie » Tue Jan 03, 2006 2:52 am

How does sympathetic stimulation impact a failing heart?
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Postby sdekivit » Tue Jan 03, 2006 10:48 am

depends on what heart failure there is. Is there a dysfunction on the left or right side of the heart ?
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Postby bionewbie » Tue Jan 03, 2006 8:33 pm

Well, doesn't a right sided heart failure will eventually affect the left side as well?

What I was thinking (please somebody verify this), is that sympathetic stimulation will cause an increase in heart rate. It will increase the heart's contractility as well as its conduction. In that case, the heart has to pump harder and faster.

However, since the heart is failing and by Starling's Law, there will be a counteractive effect on the heart as the fibers are stretched too much and too far.

Is that correct?
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Postby sdekivit » Wed Jan 04, 2006 9:52 am

bionewbie wrote:Well, doesn't a right sided heart failure will eventually affect the left side as well?

What I was thinking (please somebody verify this), is that sympathetic stimulation will cause an increase in heart rate. It will increase the heart's contractility as well as its conduction. In that case, the heart has to pump harder and faster.

correct

However, since the heart is failing and by Starling's Law, there will be a counteractive effect on the heart as the fibers are stretched too much and too far.

Is that correct?


but as sympathetic impulses are too high, you'll get a heart ischemia. Due to too fast en too hard contraction, the heart muscle will create an hypoxia.
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Postby bionewbie » Wed Jan 04, 2006 3:05 pm

sdekivit wrote:
but as sympathetic impulses are too high, you'll get a heart ischemia. Due to too fast en too hard contraction, the heart muscle will create an hypoxia.


I can understand that. So in terms of sympathetic stimulation on the heart, it will cause an increase in contractility, conduction and heart rate.

However, as the sympathetic impulses increases, it will put more strain on the failing heart will has to do more work to pump harder and faster. It will get to point where the heart won't be able to handle the extra workload, thus causing ischemia.

So I mentioned, Starling's Law before, where does that come in?
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Postby sdekivit » Wed Jan 04, 2006 3:42 pm

Starling's law says that the force of contraction increases when preload increases.

But a sympathetic inpulses increases, also (nor)adrenalin is produced in the adrenal gland. And these will cause the increased contraction in the heart.


This is because when they bind to B1-receptors, the activate a second messenger system. This results in phosphorylation of voltage-gated Ca(2+)-channels, so that they are open longer. The second effect is that phospholamban is phosphorylated and thereby increasing it's activity: pumping Ca(2+) back into the cytosol

--> with the next contraction, thus more Ca(2+) from the sarcolemma is available and thus a stronger contraction.
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