smrithi
Forum Newbie
Topics: 5
Posts: 16
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hello
wat is the effect of sympathetic nervous system stimulation on renal vessels ? how will effect the GFR?
plz explain me about this ?
thanx
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| mildus
Forum Guru
Topics: 19
Posts: 614
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Sympathetic nervous system effects both afferent and efferent arteriole diameter.
1) If there is a severe hypovolemia (pressure below e.g. 50mm Hg), there is a strong activation of sympathetic nervous system. Sympathetic fibers cause vasoconstriction of renal vessels (both aff. and eff. arteriole, especially afferent arteriole) thus decreasing GFR and shifting blood from the kidney to the heart and the brain where it is more important in that moment. (This is how Sy decreases or even stops(!) GFR in order to survive; GFR autoregulation is absent in this case)
2) If there is a slight hypovolemia, hyponatremia or hypotension, sympathetic nervous system will be slightly activated, but renal autoregulation is stronger so GFR remains constant. It can also be said that sympathetic system then helps in stimulating renin secretion which will result in efferent arteriole vasoconstriction due to angiotensin, and there will be reflex vasodilatation of afferent arteriole, so GFR remains constant in spite of hypotension, but angiotensin will also act upon all systemic arterioles leading to their vasoconstriction and increase blood pressure (also by aldosterone dependent water and sodium reapsorption).
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| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
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very well explained mildus...
to add more
and there re two ways kidney autoregulates, by the myogenic mechanism, and the other way is by constriction or dilatation of the arterioles... and the gfr will remain constant from 80 to 180 mm hg. ie from any change from 80 to 180 mm hg, the gfr will remain constant in the kidneys due to autoregulation...
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