15. Calculation of reabsorption and secretion rate

Question 1

Filtered lto eoad - calculation

Answer 1

GFR x plasma concentration

Question 2

excretion rate - calculation

Answer 2

urine flow rate ( ml /min ) x urine concentration

Question 3

renal - how to estimate secretion

Answer 3

Secretion = excreted- filtered

Question 4

renal how to estimate urinary excretion

Answer 4

urinary excretion = glomerular filtration - tubular reabsorption + tubular secretion

Question 5

FENa ?

Answer 5

fractional excretion of sodium

Question 6

fractional excretion of sodium (FENa)

Answer 6

ti is the percentage of the sodium filtered by the kidney which is excreted in the urine

Question 7

fractional excretion of sodium (FENa) - calculation

Answer 7

Na+ excreted / Na+ filtered = (urine flow rate x urine concentration of Na+ ) / (GFR x plasma concentration of NA+ ) = ( urine flow rate x urine concentration of Na+ ) / ( Ucr x V /Pcr x plasma concentration of Na+ ) = ( Pcr x UNa) / ( UCRr x P Na)

Question 8

• What is the formula for filtered load?

Answer 8

Filtered load = glomerular filtration rate × Px ( Px is the plasma concentration of X)

Question 9

• With respect to kidney fluid dynamics, excess filtration compared to excretion leads to ____ (reabsorption/secretion).

Answer 9

Reabsorption

Question 10

• A patient’s GFR is 125 mL/min and plasma concentration of substance X is 20 mg/mL. What is the filtered load of X (mg/min)?

Answer 10

Filtered load = GFR × plasma concentration = 125 mL/min × 20 mg/mL = 2500 mg/min

Question 11

• A patient’s urine flow (V) is 5 mL/min. X is found in his urine at a concentration of 1000 mg/mL (UX). Find the excretion rate (mg/min).
n

Answer 11

Excretion rate = V × UX = 5 mL/min × 1000 mg/mL = 5000 mg/min

Question 12

• For X, a patient’s filtered load is 100 mg/min and excretion rate 200 mg/min. Is X reabsorbed or secreted?

Answer 12

Secreted (secretion rate = excreted - filtered = 200 mg/min - 100 mg/min = 100 mg/min)

Question 13

• For Y, a patient’s filtered load is 30 mg/min and excretion rate is 20 mg/min. Is Y reabsorbed or secreted?

Answer 13

Reabsorbed (reabsorption rate = filtered - excreted = 30 mg/min - 20 mg/min = 10 mg/min)