Q: Which formula is used to calculate the clearance ($$C_x) of a $$substance from plasma?

$$C_x = \frac{U_x \times V}{P_x}$$

Q: A patient has a urine flow rate of $$2\ \text{ml/min}$$, a urine inulin concentration of $$15\ \text{mg/ml}$$, and a plasma inulin concentration of $$0.3\ \text{mg/ml}. $$What is the GFR?

$$GFR = \frac{2 \times 15}{0.3} = 100\ \text{ml/min}$$

Question 1

Which of the following best describes renal clearance?

Accepted Answer

The rate at which a solute is excreted from the body by the kidneys.

Question 2

Which formula is used to calculate the clearance ($$C_x) of a $$substance from plasma?

Accepted Answer

$$C_x = \frac{U_x 	imes V}{P_x}$$

Question 3

In the context of renal clearance, what does $$U_x$$ represent in the formula $$C_x = \frac{U_x 	imes V}{P_x}$$?

Accepted Answer

Urine concentration of the substance

Question 4

Which property makes inulin an ideal marker for measuring glomerular filtration rate (GFR)?

Accepted Answer

It is freely filtered, not reabsorbed, and not secreted by the nephron.

Question 5

A patient has a urine flow rate of $$2\ 	ext{ml/min}$$, a urine inulin concentration of $$15\ 	ext{mg/ml}$$, and a plasma inulin concentration of $$0.3\ 	ext{mg/ml}. $$What is the GFR?

Accepted Answer

$$GFR = \frac{2 	imes 15}{0.3} = 100\ 	ext{ml/min}$$

Question 6

Which of the following is TRUE regarding the mass balance concept in renal physiology?

Accepted Answer

The mass of a substance entering the kidney equals the mass leaving the kidney via urine and venous blood.

Question 7

Which of the following substances is commonly used to estimate renal plasma flow (RPF) because it is freely filtered and almost completely secreted?

Accepted Answer

Para-aminohippuric acid (PAH)

Question 8

Which Starling force opposes filtration in the glomerular capillaries?

Accepted Answer

Oncotic (colloid osmotic) pressure of the capillary plasma

Question 9

Which of the following would most likely increase glomerular filtration rate (GFR)?

Accepted Answer

Dilation of the afferent arteriole

Question 10

A patient’s plasma creatinine is elevated, but their blood urea nitrogen (BUN) is normal. What does this most likely indicate?

Accepted Answer

Reduced GFR due to decreased renal function

Question 11

Which cell type in the glomerulus can contract to alter the surface area available for filtration?

Accepted Answer

Mesangial cells

Question 12

Which mechanism is responsible for intrinsic autoregulation of GFR in response to increased arterial blood pressure?

Accepted Answer

Myogenic response (Bayliss effect)

Question 13

What is the role of the macula densa in tubuloglomerular feedback?

Accepted Answer

It senses NaCl concentration in the distal tubule and signals afferent arteriole constriction.

Question 14

Which of the following would decrease renal blood flow (RBF)?

Accepted Answer

Activation of sympathetic nerves causing vasoconstriction of afferent arterioles

Question 15

Which equation correctly relates renal plasma flow (RPF) to renal blood flow (RBF) using hematocrit ($$Hct$$)?

Accepted Answer

$$RBF = \frac{RPF}{1 - Hct}$$

Question 16

Which of the following is NOT a component of the glomerular filtration barrier?

Accepted Answer

Mesangial cell cytoplasm

Question 17

A drug is filtered by the glomerulus, partially reabsorbed, and partially secreted. Which clearance equation should be used?

Accepted Answer

General clearance equation: $$C_x = \frac{U_x 	imes V}{P_x}$$

Question 18

Which hormone causes vasoconstriction of renal arterioles, thereby decreasing GFR and RBF?

Accepted Answer

Angiotensin II

Question 19

Which of the following best explains why plasma creatinine is a better estimate of GFR than plasma urea?

Accepted Answer

Creatinine is filtered and minimally reabsorbed or secreted, while urea is reabsorbed.

Question 20

Which of the following would most likely result from a decrease in the filtration coefficient ($$K_f) of $$the glomerulus?

Accepted Answer

A decrease in GFR

Renal Clearance and Glomerular Filtration Rate: Mechanisms and Measurement

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