Q: What is the formula for clearance of a solute X from the blood?

$$\text{Clearance of X} = \frac{\text{excretion rate of X}}{[X]_{plasma}}$$

Question 1

Which of the following best describes the primary function of the glomerular filtration barrier in the renal corpuscle?

Accepted Answer

It filters blood plasma based on size and charge, preventing cells and most proteins from entering the filtrate.

Question 2

Which pressure is primarily responsible for driving filtration in the glomerulus?

Accepted Answer

Blood hydrostatic pressure ($$P_{GC})$$

Question 3

A patient has a plasma creatinine concentration of 0.01 mg/mL, a urine creatinine concentration of 1.25 mg/mL, and a urine flow rate of 1 mL/min. What is the estimated glomerular filtration rate (GFR)?

Accepted Answer

125 mL/min

Question 4

Which segment of the nephron is responsible for the majority of reabsorption of ions, nutrients, and water?

Accepted Answer

Proximal tubule

Question 5

If the efferent arteriole constricts (before compensation), what happens to renal blood flow, glomerular capillary pressure, and GFR?

Accepted Answer

Decreases, increases, increases

Question 6

Which of the following substances is normally 100% reabsorbed in the nephron, resulting in a clearance rate of 0 mL/min?

Accepted Answer

Glucose

Question 7

What is the formula for clearance of a solute X from the blood?

Accepted Answer

$$	ext{Clearance of X} = \frac{	ext{excretion rate of X}}{[X]_{plasma}}$$

Question 8

Which process in the nephron is most similar to secretion, based on the movement of substances across epithelial cells?

Accepted Answer

Reabsorption, because in both, substances cross epithelial cells lining the peritubular capillaries and epithelial cells lining the nephron tubule.

Question 9

Which of the following best explains why glucose appears in the urine of a patient with diabetes mellitus?

Accepted Answer

The transport maximum ($$T_m) $$for glucose reabsorption is exceeded, so excess glucose is not reabsorbed and is excreted.

Question 10

Which of the following is the primary driving force for most renal reabsorption?

Accepted Answer

Active transport of Na$$^+ by Na$^+/K$^+-$$ATPase and Na$$^+$$ symports

Question 11

A patient’s plasma X concentration is 0.02 mg/mL, urine X concentration is 12 mg/mL, and urine flow rate is 1 mL/min. What is the clearance of X, and is X net reabsorbed or net secreted? (GFR = 125 mL/min)

Accepted Answer

60 mL/min; net reabsorbed

Question 12

Which of the following statements about local autoregulation of GFR is correct?

Accepted Answer

GFR remains constant between 80-180 mm Hg mean arterial pressure due to myogenic response and tubuloglomerular feedback.

Question 13

Which of the following is NOT filtered through the glomerular filtration barrier under normal conditions?

Accepted Answer

Plasma proteins

Question 14

Which of the following best describes the effect of peritubular capillary pressures on reabsorption?

Accepted Answer

Low hydrostatic pressure and high colloid osmotic pressure favor reabsorption of fluid into the capillaries.

Question 15

Which of the following is true regarding the clearance of penicillin?

Accepted Answer

Penicillin clearance is greater than GFR due to net secretion.

Question 16

Which formula correctly expresses the filtration rate of a solute X?

Accepted Answer

$$[X]_{plasma} 	imes 	ext{GFR}$$

Question 17

Which of the following mechanisms is involved in the tubuloglomerular feedback for autoregulation of GFR?

Accepted Answer

Macula densa cells detect increased flow and signal afferent arteriole constriction via paracrine signaling.

Question 18

Which of the following is a consequence of renal transport saturation for glucose?

Accepted Answer

Glucose appears in the urine because transporters cannot reabsorb all filtered glucose.

Question 19

Which of the following best describes the relationship between clearance and GFR for a substance that is neither reabsorbed nor secreted?

Accepted Answer

Clearance equals GFR

The Kidneys: Filtration, Reabsorption, Secretion, and Renal Function

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