Lecture 4: Clearance - FEna

Question 1

What is the equation used for input via renal artery?

Answer 1

Input = P^a_x x RBF^a

• P^a_x = arterial concentration of X (mg/ml)
• RPF^a = renal arterial plasma flow (ml/min)

Question 2

What is the equation used for output via renal vein?

Answer 2

Venous effluent = P^V_x x RPF^v

• P^V_X = renal vein plasma concentration of x (mg/min)
• RPF^v = renal plasma flow rate of vein (ml/min)

Question 3

What is the equation for urinary excretion rate?

Answer 3

Urinary excretion_x = U_x x V

• U_x = urine concentration of x (mg/ml)
• V = urine flow rate (ml/min)

Question 4

What is the equation for renal clearance?

Answer 4

C_x = U_x * V(dot) / P_x

• U_x = urine concentration
• Vdot = urine flow rate
• P_x = plasma concentration

Question 5

If a substance is freely filtered but neither reabsorbed nor secreted, the renal elimination rate (i.e., clearance) equals what?

Answer 5

GFR

Question 6

What are the 5 requirement of a substance suitable for measurement of GFR?

Answer 6

1. Freely filtered across the glomerulus –> not bound to plasma proteins
2. Undergoes no tubular reabsorption
3. Undergoes no tubular secretion
4. Is neither metabolized nor synthesized in kidney
5. Does not alter the GFR

Question 7

What is the gold standard exogenous substance for measuring GFR?

Answer 7

Inulin

Question 8

What is the endogenous water soluble substance that is freely filtered but neither reabsorbed nor secreted?

Answer 8

Creatinine

Question 9

Which concentration of creatinine is approximately proportional to GFR?

Answer 9

Plasma concentration

Question 10

Which substance is filtered and secreted but not reabsorbed from the plasma during passage through the kidney?

Answer 10

Para-amino hippurate (PAH)

Question 11

The clearance of PAH is equal to?

PAH is used to measure?

Answer 11

• Equals renal plasma flow
• PAH is used to measure effective RPF

Question 12

What is the clearance limitation for PAH?

Answer 12

Works for low plasma concentrations only, tubular carriers saturate at 80 mg/mL plasma

Question 13

What is the equation for RPF and RBF?

Answer 13

• RPF = (1-Hct) x RBF
• So… RBF = RPF/(1-Hct)

Question 14

What is the equation of filtered load (FL)?

Answer 14

FL = GFR x P_x

Question 15

What is the equation for Excreted Load (EL)?

Answer 15

EL = V x U_x

Question 16

If the Filtered Load (FL) > Excreted load (EL) this means what?

Answer 16

There is net reabsorption of the filtered solute

Question 17

If the Excreted load (EL) > Filtered Load (FL) this means what?

Answer 17

There is net secretion of the filtered solute

Question 18

What is the equation for Filtration Fraction (FF)?

Answer 18

FF = GFR/RPF, ~20%