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Renal clearance of substance X
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Volume of plasma from which X is completely cleared by the kidneys per unit time
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Equation for clearance
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Cx = Ux * V / Px
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Definition of GFR
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Rate at which plasma is filtered by the renal glomerular capillaries
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Reasons inulin is a good substance to measure GFR
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1. freely filtered by the golmeruli and only the glomeruli2. not reabsorbed or secreted by the kidney tubules3. not synthesized, destroyed or stored by the kidney4. nontoxic
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Definition and calculation of filtered load
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The amt of substance filtered per unit timefiltered load = Px * GFR
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Effect of inulin not being reabsorbed, secreted, stored, etc by the kidneys
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Filtered inulin equals excreted inulin
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Equation for excretion of substance X
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Ux * V
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Why does inulin clearance equal GFR?
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Setting filtered inulin equal to excreted inulin and solving for GFR, you get:GFR = UIN * V / PIN = CIN
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Causes of error in using creatinine to measure GFR
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Creatinine is filtered and also secreted by the kidney, causing a 20% increase in the numerator of clearancecolorimetric method measures other plasma proteins as well, leading to a 20% increase in the denominatorthese errors cancel out, leading to a good ESTIMATE of GFR when it is about normal
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Effect of reduced GFR on using creatinine to estimate GFR
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Creatinine clearance will overestimate GFR due to high levels of plasma creatinine
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Effect of drugs inhibiting tubular secretion of creatinine or raise plasma conc of other proteins on using creatinine to estimate GFR
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Creatinine clearance will underestimate GFR
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Relationship b/w GFR and plasma creatinine
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Inverse
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Impact of body type on plasma creatinine levels
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A person w/ higher muscle mass will have a higher level of plasma creatinine
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Equation for RBF
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RBF = RPF / ( 1 - hematocrit )
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Equation for RPF
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RPF = Cpah / Epahwhere C is the clearance of PAH and E is the extraction ratio for PAH
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