Flashcards in Renal Clearance Deck (20):
what is clearance?
the volume of plasm cleared of a substance by the kidney in a unit of time
amount excreted / plasma concentration
Cx = (Ux*V)/Px
what are characteristics of GFR markers?
- freely filtered (filtrate conc = plasma conc)
- neither reabsorbed or secreted
- not metabolized by cells
- accurately measureable
what are common GFR markers?
cystatin C--NOT present in urine- degraded in tubules
what is the filtered amount?
GFR * plasma conc = filtered load
what is the definition of kidney failure in terms of GFR?
<25% of normal GFR
what is a draw back of using creatinine to measure GFR?
cannot detect acute renal failure because of a lag in measurements
what affects creatinine?
aging- decrease GFR
pregnancy- increase GFR
body composition- muscle mass present
what is fractional clearance?
ratio of substance clearance to inulin clearance
what is the fraction clearance of a GFR marker?
Cx / Cin = 1
what is the fractional clearance of a secreted substance?
Cx/ Cin > 1
what is the fractional clearance of an absorbed substance?
Cx / Cin < 1
what is tm? what substances have it?
saturation level of an organic substances- determined by the number of transporters present
what is PAH? what is it used for?
used to measure renal plasma flow
Cpah = total RPF
what is the Fick method of renal plasma flow? why is it different?
takes into account the extraction efficiency for PAH
divides Upah * V by the difference in afferent and efferent arteriole concentrations of the substance (rather than plasma concentration)
how is the amount of water absorbed in the tubules determined?
U/P ratio for inulin
U/P = 1 no water reabsorption
U/P = 2 50% water absorbed
U/P = 100 99% of water reabsorbed
what is the percent of water reabsorbed?
100 - [100/(U/P)in]
what is the normal range of water reabsorption?
U/P = 50-100
(1% of filtered water is excreted)
what is free water clearance?
volume of plasma completely cleared of our water per unit time
CH2O = V - Cosm
Cosm = Uosm * V / Posm
what is positive free water clearance?
urine is hyposmotic
remaining body fluids are concentrated