DSL - Renal Clearance

Question 1

What is GFR?

Answer 1

Amount of fluid filtered from the glomerulus into Bowman’s capsule per unit time.

Question 2

Uses of clearance tests

Answer 2

1. To calculate GFR
2. To measure RPF
3. To study the renal handling of substances
4. To study the concentrating power of the kidney by measuring free water clearance

Question 3

What is filtration fraction?

Answer 3

The percentage of renal plasma flow (RPF) that is filtered across the renal glomerular capillaries

Question 4

What is filtration load?

Answer 4

The amount of a substance X that is filtered by the glomerulus per unit of time

Question 5

What is the normal range of GFR?

Answer 5

GFR of 60 or higher is the normal range.

Question 6

What do the abnormal values of GFR mean?

Answer 6

• GFR below 60 means kidney disease

- GFR of 15 or lower means kidney failure

Question 7

What are the factors determining GFR?

Answer 7

1. filtration forces acting

Question 8

State the normal clearance values of glucose, urea, creatinine, water, inulin, PAH, HCO3 with the reasons why these substances get these clearance values.

Answer 8

a) Glucose: 0 because all reabsorbed in PCT
b) Urea: 75 ml/min; that is less than GFR because 60% reabsorbed
c) Creatinine: 140 ml/min; that is similar to GFR because not reabsorbed but secreted
d) Water: 1 ml/min; 99.4% reabsorbed in tubules
e) Inulin:125 ml/min: not secreted and not reabsorbed, just filtered
f) HCO3: 0, all reabsorbed

Question 9

What is the formula used to calculate GFR?

Answer 9

GFR = (Us x V)/Ps = Cs