young_doc
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Which of the following regarding Sympathetic to the heart is False?
a. stimulation causes an increased heart rate
b. stimulation causes an increasd contractility
c. stimulation causes dilation of the coronary arteries
d. post-ganglionic fibers arise from the cervical and thoracic ganglia
e. pre-ganglionic fibers arise from all cervical and thoracic spinal cord segments
E is clearly wrong. But since when does sympathetic stimulation cause coronary vasodilation? What's the mechanism? What receptor is it acting on? Can anyone explain why C is true?
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| icemaiden
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maybe because of autoregulation. Sympathetic stimulation increases the metabolic activity of the heart and the only way to increase O2 supply is by increasing the blood flow----which is by vasodialation by release of adenosine.
ice
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| young_doc
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makes sense. i was just wondering if there was a direct vasodilatory sympathetic effect on the coronary arteries. Because if there was i had never heard of it!!!
Thanks ice.
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| khorshid
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Eventhough that's reasonable, but I think you can't count it as a sympathetic effect in this Q.So both C and E are wrong? young-doc may I ask you where is the Q from?
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| icemaiden
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or it could be because of beta2---which is vasodialatory to all blood vessels.
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