Renal 4 Flashcards
what is clearance
rate at which a solute disappears from the body by excretion or metabolism
clearance of x(ml/min)=
excretion rate of x (mg/min)/ (x) plasma (mg/ml)
clearance is expressed as what
the volume of plasma passing through the kidneys that has been totally cleared of solute in a given period of time (usually min)
- blood cleared of solute
1mg of solute Z in 100ml of plasma, found 0.5mg of Z appearning in urine/min
clearance of z= 0.5mg/min / 1mg/ml
= 50ml/min
- kidneys removes all solute Z in 50ml of plasma in one minute
how do we most accurately calculate GFR
look at clearance of substance that is freely filtered and neither reabsorbed or secreted
what is perfect molecule to measure clearance
inulin
- method is impractical
what is inulin
polysaccharide found in isolated nephrons to be completely filtered and not reabsorbed
what do clinicians commonly use to measure GFR and renal function
creatinine clearance
Why is creatinine not the most accurate
freely filtered but is also secreted in very small amounts
- slightly overestimates GFR
person has plasma creatinine conc. of 0.01mg/ml and an excretion rate of 1.25mg/min
1.25mg/min / 0.01 mg/ml = 125 ml/min
once we know an individuals GFR what can we look at
how their kidneys handle any filtered solute by measuring the solutes plasma conc. and excretion rate (collecting urine and blood)
filtered load of X=
[x]plasma x GFR
how can we tell how the nephron handled the substance
comparing the filtered load with its excretion rate
if less substance appears in the urine then filtered,
net reabsorption has occured
if more appears in the urine than was filtered,
net secretion has occured
what else can we compare GFR to
clearance of a solute
what is renal clearance
non-invasive method using collected urine and blood
what is purpose of renal clearance
- calculate GFR - if substance is filtered, not reabsorbed nor secreted (filtered=excreted)
- understand the net renal handling of any filtered solute
if clearance of a substance is less than GFR
Net reabsorption
if clearance of a substance is greater than GFR,
net secretion has occurred
what does comparison of clearance values only give you
net handling of a solute
- net reabsorption or net secretion
GFR=clearance
Filtered=excreted
filtered, not reabsorbed, not secreted
GFR>clearance
filtered>excreted
e.g., urea and glucose
filtered and net reabsorption
GFR<Clearance
filtered<excreted
e.g., penicillin
filtered and net secretion
