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Old 12-26-2012
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Vascular Angiotensin Effects on Renal Vessels!

need help with this concept, its a little blurry right now:

At HIGH levels, Angiotensin II constricts both vessels; but Efferent > Afferent.

1) RPF is decreased (obvious)
2) GFR is also decreased (because of afferent constriction),
3) But GFR is decreased 'less', because protective effect of efferent vasoconstriction.

***But if Efferent arteriole is vasoconstricted MORE than Afferent, then wouldn't the decrease in GFR be negated (and conversely increased again) by the more pronounced vasoconstriction at the efferent end?
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A increased filtration fraction
Here as u already mentioned ang 2 constricts efferent more than afferent so increases gfr and decreases renal plasma flow which from equation = increased FF=gfr/rpf

D increased K excretion
In this example decreased bp will cause increased secretion of renin/ang/aldosterone
Later increasing Na absorption and K excretion
Note that GFR decreases and ang 2 is released to maintain close to normal gfr
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Last edited by MedicalExaminer; 12-26-2012 at 12:59 PM.
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Originally Posted by MedicalExaminer View Post
A increased filtration fraction
Here as u already mentioned ang 2 constricts efferent more than afferent so increases gfr and decreases renal plasma flow which from equation = increased FF=gfr/rpf

D increased K excretion
In this example decreased bp will cause increased secretion of renin/ang/aldosterone
Later increasing Na absorption and K excretion
Note that GFR decreases and ang 2 is released to maintain close to normal gfr

thanks medicalexaminer. i understrand why FF is correct. but wouldn't choice e) decreased RBF ALSO be correct? whenever you have constriction of the afferent arteriole, and/or efferent arteriole, you will ALWAYS get decreased RPF.

and a decrease in RBF can be implied from a decrease in RPF, right?
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Originally Posted by ReggieMiller View Post
thanks medicalexaminer. i understrand why FF is correct. but wouldn't choice e) decreased RBF ALSO be correct? whenever you have constriction of the afferent arteriole, and/or efferent arteriole, you will ALWAYS get decreased RPF.

and a decrease in RBF can be implied from a decrease in RPF, right?
Agree on ur statement that option D is also correct
But i guess choice A would be more likely the answer cause it includes both-changes in gfr and rpf in one equation
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Yes both are the same with little differences in physiologic terms
To be more precise RBF is proportional to RPF
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thanks again for clarifying!
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U are welcome
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