Glomerular Filtration II

Question 1

What is renal clearance?

Answer 1

Volume of plasma from which all of a substance has been removed and excreted into urine per unit time

Question 2

How is GFR measured?

Answer 2

By measuring the renal clearance of inulin

GFR = Uin x V/Pin = Cin

U = concentration in urine

V = urine flow

P = concentration of substance in plasma

Question 3

What endogenous substance can be used to approximate GFR?

Answer 3

Creatinine

However it slightly overestimates GFR

Can be used to follow a patient over a long period of chronic renal disease

Question 4

What does a change in inulin concentration in the nephron relative to plasma reflect?

Answer 4

Changes in water movement because the amount of inulin filtered does not change as it moves down the length of the tubule

Question 5

What is the single ratio?

Answer 5

BSin/Pin = 1 = TFin/Pin

Question 6

What is fractional excretion?

Answer 6

Fraction of the filtered mass of a substance that the excreted mass represents

Common way of calculating the degree of net reabsorption or net secretion

(Ua x V)/(GFR x Pa) = FEa

Question 7

What does the value of Fractional excretion represent?

Answer 7

If above 1 - net reabsorption

If below 1 - net secretion

Question 8

What is the double ratio?

Answer 8

(Ua/Pa)/(Uin/Pin)

(TFa/Pa)/(TFin/Pin)

Used to evaluate the presence of net reabsorption or net secretion in individual nephron segments