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28 Cards in this Set
- Front
- Back
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what are 3 reasons we might measure GFR
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1. get an ideal of renal health
2. decreased GFR can be disease (dx) 3. Dose drugs |
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what is the filtered load, in word and mathematically
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rate that a substance enters filtrate
FL= GFR x [substance] |
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waht is teh excretion rate, formula
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rate that things are peed out
Er= Flow rate + Secretion - reabsorb ER = V u |
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if secretion and reabs rate are both 0, what does excretion rate equal
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Filtered Load
Er=FL , when S and R are 0 *ex inuin ER also = V U |
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when does flow rate equal excretion rate
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when secretion and reabsorption are zero
*ex inulin, we now have flow rate from excretion rate and we can determine GFR when we know the conc of inulin GFR= Fl x [conc] |
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we know that inulin isnt secreted or absorbed and so what enters must leave. wht is the other formula for this
Er=Fl, GFR=Fr x [conc] |
GFR= ([urine] x urine rate)/[plasma]
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what is a feature of a molecule used to determine GFR? what is used experimentally, what about clinically
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freely filtered, NOT reabs OR secreted
inulin: experimental creatinine: clinical |
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why is creatinine a good marker for GFR clinically
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freely filtered, not reabs and only slight secretion
**made constantly by sk mm breakdown (we dont need to inject anythign) **in steady state in blood, if formation and excretion are stable |
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what are the 2 ways creatinine clearance is used to determine GFR
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1. Creatinine clearance: CRcl= ([Cr urine] x urine flow rate)/[Cr in plasma] must collect the urine (UV/P)
2. use plasma conc of Cr in an equation. cockcroft, MDRRD |
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if you want to use creatinine to determine GFR by collecting urine how is this done
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GFR=Cr clearnace= [Cr in pee] x pee rate/[Cr in plasma]
(UV/P) **measure urine for 24 hrs BORING, better to use an equation online Cockcroft-Gault |
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determine GFR:
urine flow = 2.0 Urine [Cr]= 0.6 plasma [Cr]= 0.01 |
GFR=Cr clearance= UV/P
2 x 0.6/0.01 120 **can also use Pcr by itself if you dont know urine flow rate or urine Cr conc with cockcroft equation or MDRD4 |
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how is GFR estimated if you know Pcr and nothing else
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formula
CockCroft-gault MRDR 4 |
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in general, if Pcr levels are high what happens to GFR
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low, inverse relationship
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what is BUN, can it estimate GFR
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Urea/Nitrogen in blood due to aa catabolism
**half of urea is reabs so NOT a good GFR BUT... BUN:Cr ratio is good to estimate GFR |
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what is the BUN:Cr ratio
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amt of urea produced from aa catabolism: Cr in plasma
**high indicates low GFR, dehydration, upper GI bleed, **normal can still be pathologic **low: increase Cr due to sk mm injury or decrease bun due to liver disease or malnutrion |
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btwn BUN and Cr what is more sensitive to changes in GFR
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BUN
BUN is more sensitive to decreases in GFR so the ratio will tell us something abotu the GFR |
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what is the clearance equation
what is clearnace in words |
C= [U] V/ [P]
something is cleared when urine conc times urine flow is divided by plasma conc volume of plasma that is cleared of a solute per minute |
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how can i find out how much X is cleared from my plasma per minute
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clearance euation
C=[U] V/[P] |
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if a substance is secreted, what is its clearance value compared to GFR, what about reabs
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increased
decreased |
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determine if the following is secreted or absorbed
GFR= 125 Px= 0.02 Ux= 0.1 V= 2.5 |
first determine the clearance, and then compare it to GFR. if more is cleared than filtered we know its excreted. if less is cleared than filtered its abs
Cl= UV/P = (.1)(2.5)/(.02) = 12.5 Cl is less than GFR (125) so X is ABS |
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determine if the following is abs or secreted
GFR= 125 P= 1 U=0 V=2.5 |
C=UV/P
= 0 x 2.5/1 =0 NONE is cleared, GLUCOSE perhaps. The substance is TOTALLY reabs |
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what is a clearance ratio
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Cx/C-inulin
**inulin is not secreted or absorbed if the ratio is 1= substance is filtered but not abs or secreted less than 1: reabs, or not filtered greater than 1: filtered AND secreted |
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what does a clearance ratio of 3 mean?
0.3 |
3: substance is secreted
0.3: substance is reabsorbed ** Cx/C-inulin C= UV/P |
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PAH excretionis a measure of what
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renal plasma flow
**the amt of PAH injected is totally excreted RBF=RPF/(1-HCT) |
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renal plasma flow can be measured how? what can we determine form RPF
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by PAH excretion
NO PAH is reabs and all that isnt filtered is then secreted so all PAH is excreted and can approximate Renal Plasma Flow RBF is calc from RPF RBF= RPF/(1-HCT) |
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what do we know about the clearance of PAH
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completly cleared
**are inulin and creatinine also totally cleared |
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determine the clearance of PAH, from this determine RPF
PAH urine: 540 V= 1 Plasma: 1 |
C= 540 x 1/1
= 540 "Effective" RPF, RPF can then be used to determine RBF= RPF/(1-HCT) |
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determine RBF
HCT= 0.4 RPF= 540 (from PAH clearance) |
RBF = RPF/(1-HCT)
RBF= 540/(1-0.40) RBF= 900 |
