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Ria
Forum Elite Topics: 30 Posts: 228 |
Hi there, Ok this is renal physiology question,it souns so simple but I dont know where I am getting all confused- Ok here is the question.If the afferent artery resistance decreases more than that of the efferent,then what changes do you expect in Filtration fraction,RBF and GFR? :? :?: Look in this ok we are expecting RBF to increase but at the same time GFR also increases but then why would the filtration fraction decrease? I am going nuts :x ,I would really appreciate if any one can help me. Thanks 
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Ria
| Forum Elite Topics: 30 Posts: 228
Please help!
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mani
| Forum Guru  Topics: 104 Posts: 1400
think what would happen to the time available for filteration. does this help?
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Ria
| Forum Elite Topics: 30 Posts: 228
Hey thanks mani, but you know what in the explanation it says that the rise in GFR is less as compared to the fall in RPF thats why FF decreases. 2.they also mention that if the efferent arteriole were to have lesser resisitance than the afferent then FF would increse.Can you please explain. Thanks once again! May God bless you!
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hiwa
| Forum Newbie Topics: 16 Posts: 188
FF=GFR/RPF if both increased but the rate of inc RPF is more than GFR then the FF will be decreased. if afferent a. dilatation and eff const--> GFR max and RPF min so the FF will be highest the opposit will give u lowest FF, between the above two option we have either both aff and eff dilated or both of them constricted, FF fraction depend on the grade of dilatation or constriction between the two arteries whether infavour of incr GFR(or FF) or infavour of reduced GFR(orFF). plasma osmolality is another factor influences the equation hope this help
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hiwa
| Forum Newbie Topics: 16 Posts: 188
"Ria" wrote: Hey thanks mani, but you know what in the explanation it says that the rise in GFR is less as compared to the fall in RPF thats why FF decreases. 2.they also mention that if the efferent arteriole were to have lesser resisitance than the afferent then FF would increse.Can you please explain. Thanks once again! May God bless you! Not sure about ur second point. but possibly by decreasing RPF ONLY(GFR constant or minimally decreased) which lead to increase FF, another interpretation, as mani mentioned , decreased RPF lead to increased filtration time and lead to inc FF
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mani
| Forum Guru Topics: 104 Posts: 1400
hiwa, i didnt mean to say that FF will increase. Rather i meant that when RBF will increase time available for filteration will decrease (due to rapid flow) and hence FF will decrease. i remember i.too, saw this question but couldnt make out why increase in GFR will be less than increase in RBF
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mash
| Forum Guru Topics: 147 Posts: 1299
if resistance of afferent is decreasing more than dat of efferent===>afferent is dilated more than the eff(bcoz Resitance is inversely related to the radius^4) RBF will increase bcoz aff is dilated AND efferent arteriole is constricted(as compared to afferent ) -->stimulate renin AT sys--->further inc in RBF GFR is increased bcoz time available fr filtration will increase and aff is dilated bcoz inc in RBF> Inc in GFR FF=GFR/RBF===>FF will decrease
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Ria
| Forum Elite Topics: 30 Posts: 228
Thanks all of you guys,I think mash explains it pretty well.Now I get it,but wont you guys say that this is a preety tough question,cause I was really discouraged as I wasnt even thinking on the Rennin activation system.Anyways thanks for the help.
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mani
| Forum Guru Topics: 104 Posts: 1400
thanx mash, i get it
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mjl1717
| Forum Junior  Topics: 964 Posts: 5442
I think in addition to what Mash is saying I think its a good idea to at least remember this chart and the opposite. GFR RBF FF constriction decrease decrease no change of afferent constriction increase decrease increase of efferent increased plasma decrease no change decrease protein Sorry couldn't get the chart format.
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tonguo
| Forum Senior Topics: 29 Posts: 124
i was wondering why y'all say that increased time for filtration leads to increased GFR? GFR is a rate, the unit is volume/time (e.g. ml/min). this means if you incr time, u incr volume too and rate won't change. actually the main factor determing GFR is capillary pressure, 2nd factor is blood flow. also, is renin secreted by efferent arteriole? my long-time impression is JG cells in afferent a. instead. any advice? for the Q itself, I think FF decr becoz the resistance for renal blood flow is reduced, and blood flow rate is faster. just think of it as overperfusion, too much blood to filter and no time to do it, although the absolute amount of filterred blood incr, the proportion decr.
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mash
| Forum Guru Topics: 147 Posts: 1299
u r right dat JG cells r in AFF arteriole and they monitor pressure there P=QR if resistance in affferent arteiole is decreasing then press will also decrease--->stimulate renin AT sys--->inc renal bld flow 2) aff is dilated more than the efferent --->hydrostatic press is more in the glomerular cap--->promote filtration--->so, GFR will be more (main factor dat determines GFR is glo cap press)
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mani
| Forum Guru Topics: 104 Posts: 1400
yes tongu, i agree with u. this is what i said in my post above, agree iwth mash,s explanation as well
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Ria
| Forum Elite Topics: 30 Posts: 228
Thanks guys even I was wondering that JG appratus determines pressure in afferent arteriole.Anyways so let me get this thing straight what you all mean is there is decrease in resisntance in afferent arteriole-----> dilatation of the afferent art---->Increase bld flow(RPF) 2.Since there is increase in RPF----->increase in capp pressure therefore GFR also increases 3. FF=GFR/ RPF but here I am back to my original quest : WHY DOES RPF INCREASE MORE THAN GFR? I am sorry I thought I got it but I just dont understand.PLEASE EXPLAIN! Maybe there is some point that Iam missing,but you guys can you clear this thing up please.
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tonguo
| Forum Senior Topics: 29 Posts: 124
Ria, I think mani and I had answered ur Q already. the key factor in determining FF is blood flow. but to help u figure it out easier, try this. think about the extreme condition, blood flow incr a big deal and filtration already reached its upper limit. in this situation, when u incr RPF, there is no change in GFR (saturated), but whats increased is the 'Unfiltered plasma flow', which equals RPF-GFR. so its clear under this siutation: no change in GFR, great incr in RPF and unfiltered plasma, therefore decr in FF.
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Ria
| Forum Elite Topics: 30 Posts: 228
Thanks tonguo, I get it now,thanks for making it all that simple for me.anything I can help you with please do ask,thanks once again
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tonguo
| Forum Senior Topics: 29 Posts: 124
thank u, Ria and everyone who posted, for bringing up this challenging topic. could u take a look at my post about countercurrent multiplication? that concept drove me nuts.
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tdr
| Forum Senior Topics: 18 Posts: 70
if afferent artery resistance decrease :arrow: afferent artery be come dilates :arrow: GFR inc, RPF inc, FF no change efferent artery resistance decrease :arrow: GFR dec, RPF inc, FF dec in your Q; afferent artery resistance decrease more than that of the efferent then net change of FF decrease :?: please correct me if i'm wrong
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doc_rajan
| Forum Newbie Topics: 4 Posts: 26
No, tdr.. ur first equation is wrong.. If afferent arteriole dilates, RPF increases, GFR increases but FF decreases.. I think tonguo explained it pretty well, Read his post once again.. Just remember, whenever RPF increases, the time that the plasma spends in the glomerular capillary network decreases leading to a decrease in FF
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