| Author | 19 Posts |
RayBerg
Forum Senior
Topics: 32
Posts: 150
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1. If renal perfusion pressure does not change, which of the following changes in afferent and efferent arteriolar resistance would result in an increase in renal blood flow but no change in filtration fraction?
Afferent arteriolar resistance......Efferent arteriolar resistance
A. unchanged ….. decreased
B. decreased ….. unchanged
C. increased ….. unchanged
D. decreased ….. decreased
E. increased ….. increased
2. Which of the following statements is/are correct?
A. Filtration fraction equals glomerular filtration rate divided by renal plasma flow.
B. Tubular maximum secretion has a finite upper limit, though it exhibits a phenomenon analogous to the threshold phenomenon for reabsorption.
C. Clearance ratio equals renal clearance of one substance divided by the clearance of another substance.
D. Effective renal plasma flow is the volume of plasma flow supplied to juxtamedullary nephrons.
E. A, B, and C are correct.
3. A 100 kg man has a plasma osmolarity of 300 mOsM (milliosmolar). After he drinks 2 liters of water (and before any fluid losses) his steady-state plasma osmolarity would be approximately:
A. 270 mOsM
B. 280 mOsM
C. 290 mOsM
D. 300 mOsM
E. 321 mOsM
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| RayBerg
Forum Senior
Topics: 32
Posts: 150
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Please explain your answers
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| drduck
Forum Guru
Topics: 82
Posts: 523
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1- it has to be D......
dilitation of arterioles wjich are nothing but resistors in series....will lead to INCREASE flow thru these vessels....so in order to increse flow both resistence shud decrease...
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| drduck
Forum Guru
Topics: 82
Posts: 523
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2- this is a bit tricky....it shud be A
.i m sure about A....but option C doesnt seem to be correct....
clearance ratio of substance X is calculated by dividing renal plasma clearance of X by renal clearence of INULIN or CREAT...
i m not sure of the latter half of option B
so i go with option A...
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| drduck
Forum Guru
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3- there is some confusion....did u mean he drank isotonic water???
if yes there wont be any change in the osmolality....
supposing he is healthy....
so it has to be D
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| drduck
Forum Guru
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plz post the answers....
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| nimer1456
Forum Newbie
Topics: 1
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1. B
FF=GFR/RPF. The question ask for an increase in RPF but no change in filtration fraction. IF you dilate the afferent but leave efferent unchanged, RPF increases, GFR increases leaving FF unchanged.
2. A (I dont think C is right)
3. i dont know... I had a Q bank like this and there was only one value below 300mOsm. I dont know the calculation though...
Please post answers 
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| RayBerg
Forum Senior
Topics: 32
Posts: 150
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Answers are:
D
E - This answer was really bothering me because I don't see how A, B, C are all correct. I myself picked A
D
These questions are from McGill website which is very reputable.
Edited by RayBerg on 06/08/07 - 02:43 PM
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| peraspera
Forum Elite
Topics: 38
Posts: 233
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we have increased blood flow, renal perfusion pressure is the same.
The main factor affecting Ff is renal plasma flow ( is the same as RBF w/out erythrocytes), The longer the fluid remains in the glomerular capillar. the greater the % of fluid then tends to be filtered.As flow decreases Ff will always have tendency to increase.
#1.if we constrict afferent art. everything decreases(GFR,RPF, Glomerular filtr. press., no FF ).
#2 If we constr. effer.-GFR is up, RPF down, FF-up.
#3 We have renal perfusion pressure the same, so if we take answer E.-
Affer. increased, effer increased- we have Increased renal blood flow but no change in FF ( very high renal plasma flow tend to give a smaller filtration).
q2-A.
q3-A. He drinks 2L of H2O-he has hipoosmotic volume expansion ( ICF-up,ECF-up)The normal plasma osmolarity is in the range of 280-300 mOs/kg. So he diluted his both compartmens.
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| SILVER
DoWhatYouGotToDo!
Topics: 22
Posts: 886
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Rayberg,
but by decreasing the resistance of both afferent and efferent, won't the FF decrease? and the ques. is asking to keep the FF unchanged.
i agree that decreasing resistance of both will inc. renal flow, but then this way the FF doesn't remain unchanged, rather wouldn't it decrease??
i was thinking B
Edited by silver on 06/08/07 - 06:13 PM
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| new_n_lost
Forum Hero
Topics: 673
Posts: 6,144
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I have One Problem
To Perspera .................If by INCREASING THE Afferent & Efferent Arteriolar RESISTENCE How can the RBF inc ?? Isnt that wht Angiotensin II does ??
To Rayberg.................If By any means we r to Inc RBF while maintaining the FF then u will have to DILATE the Afferent and keep the Efferent Unchanged Which will inc the blood flow but at the same time maintain the FF
AS its already mentioned that FF is dependent on RBF the Faster the Flow the Less the Filtration
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| peraspera
Forum Elite
Topics: 38
Posts: 233
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it should be answer B.
sorry for mistake. I got the words just reversed.( increased vs decreased ).
Anyway, if someone has an idea, please make it clear explanation.
Thank you in advance.
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| me007
Forum Guru
Topics: 72
Posts: 799
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b - will incr GFR and RPF => will incr FF, which should have no change
here
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| drduck
Forum Guru
Topics: 82
Posts: 523
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about Q 1....very basic....
please see the table given in renal physiology kaplan.
very impressive.....u will never forget...
following is the ressistence of eff and aff arteriole
AFFARENT EFFERENT
renal blood flow increase decrease decrease
glomerular filtration increase decrease increase
AG II causes increase tone of both both the vessels.....increase resistence.......this is why less filtrate reaches the tubules and so less will be loss of sodium and water.....and this is what AG II does.
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| drduck
Forum Guru
Topics: 82
Posts: 523
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007......the 2 Q are different,
in ur Q they have asked u....about the RBF.....so the best possible answer is dilitation of affarent arteriole.
but to increase the RBF....that is increase flow of blood not only in the glomerulus but in the entire nephron.....this is very important....
in the Q asked by rayberg.....FF is kept constant.....
now, if we know that RBF is blood in the entire nephron.....we also know that in a nephron there is serial arrangement of ressistors that is the affarent and the efferent arterioles.....
so.....u think this way.....
one.......we decrease resistence of affarent and do nothing with the efferent.
two........we decrease resistence of both affarent and effernt....
what do we infer????
in situation two.......better flow that is increase RBF.....than the one bcos, in one there is still some resistence offered by the efferent....which deceases the RBF....
but if u ask about the glomerular filtration....
still dilation of affarent with constriction of efferent....increases GFR more than dilatation of affarent and keeping the efferent as it is....
i hope u got it.....
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| drduck
Forum Guru
Topics: 82
Posts: 523
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there shudnt be any probs with Q 1 now.....lets go for the Q 2....
do anyone has the explation??????
i mean how option B is correct.....
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| tompat
Forum Elite
Topics: 39
Posts: 345
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oh such beautiful q s, left just like that.
ok my ans are
1.D( if we play here with no.s then B cud also be right)
2.E(no doubt)
3.C(NO DOUBT about this one).
first 2 n 3 cuz i am more sure about it.
q2:we all know the definition of filtration fraction.
yes there is no doubt that tubular secretion is a transport max system and it does require a threshold.
clearance ratio is clearance of 1 sub divided by clearance of another , generally inuline clearance is taken into consideration.
Q3:
guys this involves simple calculation.
this man has drunk 2 lit of water, when it is said that 2 lit. of water it is pure water, no way ur going to asume it to be isotonic.
if 70kg man has 42 lit. of water in body a 100 kg man will have 60 lit. of water.after drinking 2 lit. of water before any compensatory mechanism sets in, his total body water wud be 62lit.
now we have 300x60=62x?
this gives?=290mosmoles.
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| tompat
Forum Elite
Topics: 39
Posts: 345
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about q 1
if we decrease both the resistances, aff n eff arteriole:
there is increase in blood flow hence plasma flow.at the same time there may be a change in GFR this is because of shear increase in the amount of plasma flowing thru glomerulus. one can argue that it wud remain constant.i cant not firmly say what exactly happens cuz its not given any where when both the arterioles dilate.
as drduck has explained that only decreasing aff. arteriole resistance wud increase GFR , there is also a chance that we will have such aff arteriolar dilation value that wud increase GFR and renal plasma flow that their ratio i.e. filtration fraction may remain constant.
though OPTION D looks better.
please express ur view guys this imp topic
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| medocuk
IM-RES
Topics: 26
Posts: 1,467
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drduck wrote:
1- it has to be D......
dilitation of arterioles wjich are nothing but resistors in series....will lead to INCREASE flow thru these vessels....so in order to increse flow both resistence shud decrease...
I agree with this answer and explanation. both resistances should decrease.
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