Renal 4 Flashcards
Define term renal clearance
The volume of plasma per unit time from which all of a substance has been removed. Removing something from the blood and excreting it through the urine. Measured in volume of plasma, notan amount of a substance excreted!
Calculate the clearance of a compound given the urine volume produced per minute, urine concentration of the compound and plasma concentration of the compound.
Clearance of X form plasma= [(Urine flow rate) x (Urine concentraion of x)]/
(Plasma concentration of X)
Explain why the clearance of inulin is a measure of GFR
Inulin is filtered but not reabsorpbed or secreted. The amount was filtered, then, will appear in the urine at the same rate that it was filtered. If a substancehas a clearance larger than inulin then it must also be secreted if lower, then some must reabsorpbed.
Explain why the clearance of creatinine is a reasonable estimate of GFR and why measuring it is easier than measuring the clearance of inulin.
Creatinine is usable because it is freely filtered and only a little bit of it is secreted. It is easier to use because do not need to IV infuse since it is a byproduct of muscle catabolism and released at a consistent rate. Also do not need to catheterize bladder so patient can collect urine over 24 hour period.
Explain why creatinine clearance as a measure of GFR becomes less accurate in a renal disease patient with very low GFR. (In such patient does the creatinine clearance over estimate or underestimate the GFR?)
The secreted fraction is about 10-20% normally of what is excreted. So a patient with low GFR, the fraction secreted will be substantially higher. The creatinine clearance more severely overestimates GFR.
Assuming creatinine production remains constant be able to explain how changes in GFR affect serum creatinine level. If told that the creatinine serum concentration is above normal state whether GFR is probably above or below normal.
if creatinine levels are above normal, GFR is likely to below normal.
If patient had renal disease that caused loss of nephrons you would expect their plasma creatinine to be high and GFR low.
Describe the variables that are used to estimate GFR using the Cockcroft-Gault equation. How could you use the estimated GFR to help in determining dosages of drugs that are excreted in the urine?
based on blood levels of creatinine, age and lean body weight
with a lower GFR you would expect less drugs to be excreted in the urine (think the definition of GFR and clearance)
Describe the variables that are used to estimate GFR using the Modification of Diet in Renal Disease (MDRD) study.
Creatinine serum levels, age, african american, and gender
Describe the effect of age on the number of functional nephrons, and GFR. How do hypertension and diabetes mellitus affect renal function changes with age?
10% decrease in functional nephrons each 10 years after 40 causing progressive decline in renal blood flow and GFR. There is more rapid decline in those with hypertension and diabetes mellitus.
