3_HST110 Clearance 2017

Question 1

What are 2 nitrogenous wastes generated by metabolism and removed by the kidneys?

Answer 1

Urea and creatinine

Question 2

What is the general relation between the ingestion/production and excretion of a substance for homeostasis?

Answer 2

Rate of excretion parallels rate of ingestion/production

Question 3

What is it called when a substance is removed from the blood and excreted in the urine?

Answer 3

Renal clearance

Question 4

What is the formal definition of renal clearance?

Answer 4

The volume of plasma per unit time from which ALL of a substance is removed by the kidneys

Question 5

What are the units of clearance?

Answer 5

mL/min (volume per time) NOT amount/time

Question 6

The rate at which the kidneys excrete a solute into the urine (X) the rate at which the solute disappears from the plasma provided that the kidney does not (Y) the solute.

Answer 6

X = equals
Y = synthesize, degrade, or store

Question 7

For any solute X that the kidney does not synthesize, degrade, or store, the only route of entry to the kidney is the (X), and the only 2 routes of exit are the (Y)

Answer 7

X = renal artery
Y = renal vein and ureter

Question 8

What is the relationship between arterial input, venous output, and urine output of the kidney based on the mass balance principle?

Answer 8

Arterial input of X =
Venous output of X +
Urine output of X

Question 9

What is the clearance equation general mass formula in terms of concentrations and flow rates?

Answer 9

PRPF (artery) = PRPF(vein) + U*V’(urine)

mmol/L)(mL/min

Question 10

What is the general clearance equation?

Answer 10

C_x = (U_x * V’)/(P_x)

Clearance rate from blood

Question 11

To calculate clearance, you need to know only 3 variables:

Answer 11

• Concentration of X in the urine
• Concentration of X in the systemic blood plasma
• Volume of urine formed in a given time

Question 12

Inulin is (X) filtered and is neither reabsorbed nor (Y) by the nephron. All inulin filtered is excreted into urine

Answer 12

X = freely
Y = secreted

Question 13

What is the relationship between filtered, secreted, reabsorbed, and excreted quantities in urine?

Answer 13

Amount filtered
\+ Amount secreted
=
Amount reabsorbed
\+ Amount excreted

Question 14

What compound is used to determine GFR in the clinic?

Answer 14

Inulin. Inulin clearance (mL/min) = GFR since it is freely filtered

Question 15

What are the 4 criteria for using the clearance of a substance to measure GFR?

Answer 15

1. Substance must be freely filtered at the glomerulus.
2. Substance must neither be reabsorbed nor secreted by the tubular system.
3. Substance must not be synthesized, degraded, or stored by the kidney.
4. Substance must not alter renal function.

Question 16

What compound is used to estimate renal plasma flwo (RPF) due to the fact that it is freely filtered AND secreted by the tubular system?

Answer 16

PAH (Para-aminohippurate)

Clearance PAH > GFR due to secretion

Question 17

If a filtered substance is completely removed from the nephron by either reabsorption or degradation, then none of the substance will be excreted in the urine, and therefore renal clearance is (X)

Answer 17

X = zero

Question 18

What are some examples of 0 clearance solutes?

Answer 18

Insulin (filtered but degraded), Glucose, amino acids, Na+ (reabsorbed)

Question 19

What are results of the comparisons of clearance of a substance X with GFR (inulin determined)

Answer 19

If CX = GFR -> No net reabsorption or secretion of X

If CX > GFR -> Net secretion of X

If CX < GFR -> Net reabsorption of X

Question 20

What is the expression for fractional excretion of a solute?

Answer 20

Defined as the ratio of the amount excreted in the urine (UX x V’) to the filtered load (PX x GFR)

FE_x = (UX x V’)/(PX x GFR) = (C_x)/GFR = (C_x)/(C_inulin)

FE < 1 = net reabsorption
FE > 1 = net secretion

Question 21

For routine GFR assessment, inulin clearance is invasive, so (X) clearance is used instead

Answer 21

X = creatinine

Question 22

Creatinine is (X) filtered and is not reabsorbed, but it is secreted to a small extent by the (Y)

Answer 22

X = Freely
Y = Proximal Tubule

Question 23

Creatinine clearance (CrCl) overestimates GFR by what percentage in healthy individuals?

Answer 23

10-20%

Question 24

What is used in common practice to determine GFR?

Answer 24

Plasma creatinine levels. Inverse relationship with clearnance

Question 25

What is the normal Creatinine range?

Answer 25

0.7 - 1.3 mg/dL