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amount of plasma filtered
25%-filtrate in glomerulus goes to urine, rest to efferent arterioles, forced in due to pressure difference, forced out of capillaries and into bowman's capsule
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primary determinant of arterial tone
PGs, overrides effect of AT II normally, causes vasodilation, more blood flow, more filtrate produced, increases GFR, ATII vasoconstriction decreases amt of blood entering and decreases GFR
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drugs that affect arteriole tone
NSAIDs-inhibit PG synthesis, increase arterial tone, vasoconstriction due to increased activity of AT II, decrease in GFR
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determinant of arterial tone and effect on GFR for efferent
ATII is primary, constriction, increase pressure and increase GFR
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drugs affecting efferent arteriole
ACE inh and ARBs, vasodilation, decrease GFR
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proximal convuluted tubule
reabsorption, major site of ammonia production, 75%
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loop of henle
reabsoption-additional 25%, concentration/diluting urine
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distal convuluted tubule
final concentration of urine, 5-10% reabsorbed
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cortical collecting tubules
reasorb NaCl and secrete K in response to aldo, reabsorb water due to ADH
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endocrine fxns of kidneys
erythropoietin, prod and secretion of renin by juxtaglomerular apparatus in response to decrease afferent arteriole pressure, decrease renal flow or increase in renal sympathetic activity
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metabolic fxns of kidney
activation of Vit D3, gluconeogenesis, metabolism of endogenous compounds and drugs (e.g. steroilds, insulin) P450 enzymes
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excretion=
filtration + secretion-reabsoprtion
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filtrated substances
H20, electrolytes, glu, small aa, creatinine
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size allowed to be filtered
less than 50 angstroms, alb 35
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molecular wt filtered
less than 20,000 daltons, alb 65,000
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charge filtered
only +, alb is -
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protein binding affect on filtered substances
only unbound, bound are secreted renally, abx, pcn, ceph
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role of tubular secretion
maintain acid base and potassium balance, H, K, NH4, organic acids and bases, creatinine, protein-bound drugs
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role of tubular reabsorption
reabsorb important compounds from filtrate back into blood
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normal urine volume
500-1600 ml/day
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specific gravity of urine
1.003-1.030, <1.010 relatively hydrated, >1.010 dehydrated
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osmolarity of urine
50-1200mOsm/kg, assesses ability of tubules to concentrate urine (fxn of ADH)
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substances not normally found in urine
glucose, protein, ketones, nitrites, lukocyte esterase, RBC, WBC and casts
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normal protein amts found in urine
<10mg/dl, alb <30mg/gm Cr
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normal amt of RBC, WBC and casts found in urine
0-1 RBC, <5 WBC and occassional cast
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factors affecting creatinine
aging, muscle mass, diseases, diet, drugs (trim, cimet, fenof increase SCr by competing with tubular secretion, chronic steroid use decreases SCr due to decrease muscle mass), tubular secreation
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24 hours creatinine clearance (ml/min)
CrCl=Ucr X V/Pcr, needs to be refrig, large possibility of error, Ucr (conc of creatinine in urine at end of collection(mg/dl), Vm urine flow rate(ml/min), Pcr concentration of creatinine in plasma at midpoint of collection
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unstable creatinine
rises by 0.5 mg/dl or more when baseline <3 mg/dl, or creatinine rises by 1 mg/dl or more when baseline creatinine is 3 mg/dl or more
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when to use MDRD (modification of diet in renal disease)
more accurate than cockcroft-gault in pts with chronic kidney disease, diabetes, or transplanted kidneys
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MDRD not validated in:
under 18 or over 70, pregnant, racial groups other than caucasians and african-americans
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when to use cockcroft-gault equation for estimating creatinine cl
older pts, better to round to 0.8 instead of 1
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when to use 24 hours urine collection for creatinine cl
prego, extreme ages and weights, pts with malnutrition, pts with skeletal muscle diseases, pts with para or quad, vegetarians and rapidly changing kidney fxn,
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compensating for amputations in cockcroft-gault
calc LBW using ht prior to amp, calc effect of limb as a % of LBW, subtract % from LBW
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% loss single, below knee
6%
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& loss, single at knee
9%
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% loss, single above knee
15%
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% loss, double below knee
12
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