Which cell in the collecting tubule functions in maintaining water and salt balance?

Correct Answer: B

Rationale: Principal cells in the collecting tubule regulate water and salt balance ADH increases water permeability (aquaporins), aldosterone boosts Na reabsorption (e.g., ENaC channels). Intercalated cells focus on acid-base H /HCO₃⁻ secretion. Macula densa cells sense NaCl JGA, not balance. Mesangial cells support glomerulus structural. Principal cells' dual role distinguishes them, critical for osmolality and volume homeostasis, unlike pH, sensing, or support cells.

Correct Answer: B

Rationale: At 150-300 mL, the bladder triggers the first urge to void stretch receptors signal (e.g., micturition reflex onset). Fullness comes at 300-400 mL escalation. Discomfort at 400-600 mL stronger stretch. Pain at 600-700 mL overdistension. Initial urge distinguishes it, critical for normal voiding cues, unlike later sensations.

Correct Answer: D

Rationale: 1% of GFR is excreted ~180 L/day filtered, ~1.8 L urine (e.g., 99% reabsorbed). 99% excreted reverses impossible. 1% reabsorbed understates most returns. 50% reabsorbed halves reality too low. Low excretion distinguishes it, critical for renal efficiency, unlike reversed or understated options.

Correct Answer: D

Rationale: A GFR marker (e.g., inulin) shouldn't be metabolized must stay intact for clearance (e.g., excreted fully). Not secreted ensures filtration-only true. Not reabsorbed keeps GFR accurate correct. Non-toxic is essential safety. Metabolism distinguishes the error, critical for marker purity, unlike filtration-only criteria.

Correct Answer: C

Rationale: CO₂ combining with H₂O via extracellular carbonic anhydrase is false occurs intracellularly (e.g., PCT enzyme). H secretion and H₂CO₃ formation are true HCO₃⁻ reclaimed. Poor permeability holds indirect reabsorption. Intracellular site distinguishes the error, key to bicarbonate mechanism, unlike correct steps.