Renal Physiology Quiz: Filtration, Reabsorption and Water Balance

Follow fluid from glomerular filtration through tubular processing. Distinguish reabsorption from secretion, then connect nephron segments and hormones with water handling.

8 questions · Estimated 6–8 minutes. Select your answer mentally, then open the explanation to check your reasoning.

1. Glomerular filtration rate (GFR) describes which quantity?

  1. The volume of urine entering the bladder each minute
  2. The total volume of blood entering the kidneys each minute
  3. The volume of fluid filtered into glomerular capsules per unit time
  4. The amount of sodium excreted per day
Show answer and explanation

Answer: C. The volume of fluid filtered into glomerular capsules per unit time

GFR measures the volume of glomerular filtrate formed per unit time, usually expressed in mL/min. It is different from renal blood flow and urine flow: most filtered water is reabsorbed before the remaining fluid is excreted.

2. Tubular reabsorption moves a substance in which direction?

  1. From tubular fluid toward the interstitium and blood
  2. From blood into the tubular lumen
  3. From the renal pelvis into the ureter
  4. From glomerular blood into the capsular space
Show answer and explanation

Answer: A. From tubular fluid toward the interstitium and blood

Reabsorption returns filtered substances from tubular fluid to the body through the interstitium and surrounding capillaries. Movement from glomerular blood into the capsular space is filtration; movement from blood into the tubule is secretion.

3. Which example represents tubular secretion?

  1. Water moving from the collecting duct into the interstitium
  2. Glucose moving from the proximal tubule toward the blood
  3. Fluid moving from glomerular capillaries into the capsule
  4. Hydrogen ions being transported into the tubular lumen
Show answer and explanation

Answer: D. Hydrogen ions being transported into the tubular lumen

Secretion adds substances to tubular fluid. Hydrogen ion secretion contributes to acid-base regulation. In contrast, reabsorption removes substances from tubular fluid and returns them toward the circulation.

4. Which segment normally reabsorbs the largest fraction of filtered sodium and water?

  1. Distal convoluted tubule
  2. Proximal tubule
  3. Collecting duct
  4. Thin ascending limb
Show answer and explanation

Answer: B. Proximal tubule

The proximal tubule normally reabsorbs roughly two-thirds of filtered sodium and water. Later segments process the remaining fluid and provide important regulation, but they do not normally perform the largest share of bulk reabsorption.

5. In a healthy person with a normal filtered glucose load, where is nearly all filtered glucose reabsorbed?

  1. Collecting duct
  2. Proximal tubule
  3. Descending thin limb
  4. Renal pelvis
Show answer and explanation

Answer: B. Proximal tubule

Glucose is reabsorbed primarily in the proximal tubule through sodium-glucose cotransport at the luminal membrane, followed by transport into the interstitium and blood. If the filtered load exceeds transport capacity, glucose can remain in urine.

6. Which statement best describes the thick ascending limb of the nephron loop?

  1. It reabsorbs water freely but no sodium chloride
  2. It filters plasma directly from glomerular blood
  3. It produces antidiuretic hormone
  4. It reabsorbs sodium chloride while remaining largely impermeable to water
Show answer and explanation

Answer: D. It reabsorbs sodium chloride while remaining largely impermeable to water

The thick ascending limb reabsorbs sodium, potassium and chloride through the NKCC2 cotransporter, but water does not follow across this segment. It helps dilute tubular fluid and establish the medullary osmotic gradient.

7. Antidiuretic hormone (ADH) increases water reabsorption in collecting duct principal cells mainly by:

  1. Increasing aquaporin-2 channels in the apical membrane
  2. Opening the glomerular filtration barrier to red blood cells
  3. Preventing all sodium reabsorption in the proximal tubule
  4. Converting water into bicarbonate
Show answer and explanation

Answer: A. Increasing aquaporin-2 channels in the apical membrane

ADH acts through V2 receptors to promote insertion of aquaporin-2 water channels into the apical membrane of principal cells. Water then moves down an osmotic gradient. The concentrating effect also depends on an adequate medullary osmotic gradient.

8. In a healthy person, a fall in ADH generally causes which change in urine?

  1. Lower volume and higher concentration
  2. Higher volume and higher concentration
  3. Higher volume and lower concentration
  4. No change in water excretion
Show answer and explanation

Answer: C. Higher volume and lower concentration

Lower ADH reduces collecting duct water permeability, so less water is reabsorbed and more dilute urine is excreted. This response helps eliminate excess water. The question assumes otherwise normal kidney function.

Further reading