Renal Physiology III

Question 1

What is Renal Clearance?

Answer 1

The removal of a given substance from the plasma by the kidney

Question 2

What is the actual definition of renal clearance?

Answer 2

the volume of plasma containing s
being completely cleared of s and excreted in the
urine per minute

Question 3

What substance can you use to calculate GFR?

Answer 3

Inulin

Question 4

How would you calculate the renal clearance of a substance?

Answer 4

concentration of the substance in the urine x volume of urine excreted in a minute over the concentration of the substance in the plasma

Question 5

The clearance of a substance which meets the following criteria will give a measure of GFR:

Answer 5

• It is freely filtered at the glomerulus
• It is not reabsorbed from the filtrate
• It is not secreted into the filtrate
• It is not metabolised by the tubular cells
• It does not interfere with kidney function - not toxic
• Easily measured

Question 6

What substance do we mainly use to calculate GFR and what is the one issue with it?

Answer 6

Creatinine, but it is secreted into the filtrate in primates

Question 7

What error is in the creatinine calculation which means we can use it to calculate GFR?

Answer 7

Because it is secreted into the filtrate, U is higher than it should be
However the test that tests for creatinine also picks up another substance in the plasma therefore P is also high and they cancel eachother out

Question 8

What is the relationship between plasma craetinine concentration and GFR?

Answer 8

GFR increases as plasma creatinine concentration decreases

Question 9

When would urea plasma concentration be noticeable?

Answer 9

Only after significant kidney damage

Question 10

When would the plasma concentration of SDMA be noticeable?

Answer 10

Only when there’s a 25-40% reduction in GFR

Question 11

What substances are used when detecting chronic renal failure

Answer 11

A combination of serum creatinine and SDMA