Sympathetic nervous system + vasoconstriction

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wu_tang_1989
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Sympathetic nervous system + vasoconstriction

Post by wu_tang_1989 » Thu Nov 30, 2006 2:05 am

Im quite confused. Since the sympathetic nervous system causes the heart rate to increase (thus more blood is pumped round the body), why do the vessels vasoconstrict? Doesn't this cause the vessels to become narrow and thus less blood can flow?

Id appreciate any help
Thank you

sdekivit
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Post by sdekivit » Fri Dec 01, 2006 7:08 pm

both are done to raise the blood pressure in respons to a low blood pressure:

1: more blood is pumped into the arterial side of the circulation
2: more blood is squeezed out of the venous side of the circulation
3: smooth muscles in the arterial wall constrict and cappilary sphincters are constricted

--> result: more circulatory blood and more resisatance leads to a higher blood pressure.

wu_tang_1989
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Post by wu_tang_1989 » Sat Dec 02, 2006 2:04 pm

so the sympathetic nervous system:

- increases heart rate
- causes vessels to vasoconstrict

and both of these things are to increase blood pressure in response to low blood pressure?


thanks for the help btw

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