3 Renal Clearance Flashcards
GFR gives a rough measure of the number of ___________.
Functioning nephrons
Decreased GFR is a key sign of ___________.
Renal disease
A reduction in GFR may indicate a disease ______________, or development of a ____________ disease.
progression; reversible
GFR determines the ___________ of chronic renal insuficiency and _______ doses of drugs secreted by kidneys.
Grading; dosages
ERx = ? (formula)
ERx = FLx + Sx - Rx
If Rx and Sx = 0, then __________.
Erx = FLx
FLx = ? (formula)
FLx = (GFR)(Px)
Conservation of mass formula: GFR = ?
GFR = (Ux)(V)/Px (“UV over P”)
The polusaccharide _______ is the gold standard GFR marker for measuring GFR, but is rarely used.
Inulin (inulin clearance = GFR)
_____________ and _____________ are frequently used as indicators of GFR in practice
creatinine clearance; plasma creatinine concentration
Why use creatinine to measure GFR?
- Produced at constant rate
- Freely filtered, not reabsorbed, and only slightly excreted
- It’s already at steady state in blood if formation and excretion are stable
- It can provide an estimate of GFR over the preceding hours
2 ways to use creatinine to estimate GFR
- Calculate creatinine clearance (Ccr) = GFR 2. Use Pcr to estimate GFR using a standard
What is the normal BUN range?
9-18 mg/dL
About ______ (fraction) of the filtered urea is reabsorbed.
1/2 (reabsorption increases when GFR is low)
Why is urea a bad GFR marker?
Because about 1/2 of it gets reabsorbed
BUN:Cr ratio should be ________
10 - 15
BUN is more sensitive to _________ than _________.
↓ GFR; plasma Cr
A high BUN:Cr occurs with _____________ (2)
Dehydration (↓ GFR) or upper GI bleed
A normal BUN:Cr occurs with _____________ (2)
Acute tubular necrosis, loss of nephrons
A low BUN:Cr ratio occurs with _____________ (3)
- Severe skeletal muscle injury (↑ Cr) 2. Liver disease (↓ BUN) 3. Malnutrition (↓ BUN)
Clearance equation:
Cx = (Ux)(V)/Px
Clearance represents the ________ of plasma that is cleared of solute X per ________.
volume; minute
Normal Cr clearance (=GFR) for females? For males?
females: 85-125 ml/min males: 97-140 ml/min (males clear faster than females)
Clearance of a secreted substance will be _________ than Ccr, thus ________ than GFR.
greater; greater (creatinine is not reabsorbed and is only slightly secreted)
Clearance of reabsorbed substances will be __________ than Ccr and _______ than GFR.
Less; less (if it’s reabsorbed there will be less being cleared) (Ex: Glucose is completely reabsorbed –> clearance is zero)
How to tell if a substance is being reabsorbed or excreted?
Calculate clearance and compare it to GFR (If less than GFR, it’s reabsorbed…..If more than GFR, it’s excreted)
All filtered glucose is _____________ by the kidney
reabsorbed
Inulin clearance ratio = _________
Cx / C(inulin)
If inulin clearance ratio = 1? < 1? >1?
ratio = 1: it mmust also be a GRF marker (filtered, but neither secereted nor reabsorbed)
ratio < 1: It’s either not filtered, or it is filtered and reabsorbed
ratio > 1: it’s filtered and secreted
__________ is an estimate of RPF, because all the blood is cleared of it.
Para-aminohippurate (PAH)
Some is filtered and the rest is excreted in urine (no PAH left in plasma leaving kidney)
Use PAH and RPF to estimate RBF
Get effective RPF from Ppah, then RPF/(1-Hct) = RBF
