Each kidney contains approximately ______ nephrons.

Correct Answer: B

Rationale: Kidneys have ~1 million nephrons not 10M, 100K, or 10K. This quantifies functional units, key for filtration capacity, contrasting with over/underestimates.

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: Prostaglandin F causes renal vasoconstriction reduces renal blood flow (RBF) and GFR (e.g., opposes vasodilators). Vasodilation (e.g., PGE/I) increases GFR opposite. Renin release is JGA-driven not direct. No effect ignores its role. Constriction's GFR drop distinguishes it, critical for prostaglandin balance, unlike dilation or neutral effects.

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.