| Terms |
Definitions |
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renal plasma flow
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RPF = 660 ml/min (for two kidneys)
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albumin's clearance and conc. in urine
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reabsorption
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in convoluted tubules, loop, collecting ducts. selective and regulated for water, sugar, AAs, and sometimes ions like sodium and magnesium. by passive diffusion and active transport. under hormonal and sympathetic control.
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PAH clearance
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filtered and strongly secreted. Cpah = RPF = 660ml/min. you can give patients this and measure clearance to determine RPF. Cpah>GFR, [urine]>plasma, [renal artery]>[renal vein]
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creatinine clearance
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filtered, not reabsorbed, very weakly secreted. [renal artery]>[renal vein], [urine]>[plasma], Ccr = 1.1GFR. this measurement is often used to estimate GFR
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compartments of body water, percentages
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intracellular (60%), extracellular: interstitial (20%), plasma (20%). all 300 mOsm/L.
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_% people show decline in GFR with age (how much)
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80%, 1ml/min/year after age 40
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filtration
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in glomerulus, non-selective (although larger particles, like albumin and blood, stay behind), amount of filtration dependent upon blood flow and pressure
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eliminate harmful substances (3)
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urea (from breakdown of AAs), urobilin (from breakdown of RBCs), some drugs (important for drug dosing - kidney functions declines with age)
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[U]x
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conc. substance X in urine
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GFR
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glomerular filtration rate = 10% RBF = 120ml/min or 200L/day
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how does increasing water intake affect GFR?
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it doesn't. blood pressure remains constant, despite water intake. if [U]x increases, then V dot decreases.
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tubular fluid
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blood pressure forces fluid into bowman's space
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what determines overall osmolarity of urine
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collecting duct
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glucose clearance
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filtered but heavily reabsorbed. Cx = 0, [glucose in urine] = 0, [renal artery]=[renal vein]
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plasma osmolarity
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~300 mOsm/L
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secretion
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in same places as reabsorption, and also selective and regulated for certain substances. entirely active transport: organic acids/bases, K+, some drugs (penicillin, morphine)
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Cx=
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([U]x x V dot)/[P]x
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lean muscle mass decreases, so
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creatinine production decreases
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renal blood flow
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RBF = 25% cardiac output = 1200 ml/min (for two kidneys)
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renal clearance
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the volume of plasma cleared of a substance (X) per unit time = Cx. example: RPF = 660, to clear 10% is Cx = 66ml/min.
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decrease in Cr production can mask _ if only [Cr] is measured
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a decrease in GFR
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what do you need to measure creatinine conc. in elderly patients
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24 hours urine collection and a blood sample
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[P]x
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conc. substance in plasma
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cleared blood
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exits via renal vein
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V dot =
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urine flow rate, ml/min
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high blood creatinine =
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low GFR
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3 hormones the kidney produces
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erythropoietin, renin, 1,25-dihydrocholecalciferol
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creatinine
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byproduct of muscle metabolism
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