renal 4

Question 1

define renal clearance

Answer 1

• substance removed from blood and excreted in urine

- clearance is the volume of plasma per unit time from which all of the substance has been removed

Question 2

calculate the clearance of a compound given the urine volume produced per minute, urine concentration of compound and plasma concentration of the compound?

Answer 2

Cx = (V*Ux)/Px

- Clearance of X = urine flow rate (V) ** urine conc. of X (Ux) / plasma conc. of X (Px)

Question 3

why is the clearance of insulin a measure of GFR

Answer 3

• insulin is freely filtered, not secreted or reabsorbed
• so amount in urine is amount that was filtered
• kidneys are only excretion route making it a great measure of GFR

Question 4

Why is clearance of creatinine a resonabile estimate of GFR and why measuring it is easier>

Answer 4

• Creatinine is freely filtered, not reabsorbed, but small amount is secreted so using this is a slight over-estimation of GFR
• constantly released into circualtion from creatine catabolism, so no IV
• don’t have to catheterize bladder either, just collect all urine over 24 hours

Question 5

is creatinine an accurate measure in patients with renal disease

Answer 5

• in renal disease, GFR is very low and secreted portion ends up being more than the normal amount of secreted creatinine
• creatinine more severely overestimates GFR

Question 6

If creatinine serum concentration is above normal state, would GFR probably be above or below normal

Answer 6

low GFR leads to high serum creatinine levels

Question 7

What are the variables used to estimate GFR using cockcrof-gault equation

Answer 7

• blood levels of creatinine, age and lean body weight

Question 8

what is the effect of age on number of function nephrons and GFR

Answer 8

• 10% decrease in number of nephrons after 40 years of age

- more rapid decline in those with hypertension or diabetes