Which of these is not usually secreted by the kidneys?

Correct Answer: A

Rationale: Creatine isn't secreted (converted to creatinine), unlike creatinine, H+ (acid-base), and penicillin (drugs). This distinguishes secretion profile, key for excretion, contrasting with metabolized compounds.

Correct Answer: A

Rationale: Countercurrent multiplier increases NaCl in the medullary interstitium, not decreases, or affects potassium. This defines concentration gradient, key for water reabsorption, contrasting with potassium roles.

Correct Answer: A

Rationale: PCT removal halts reabsorption (65% filtrate), stopping urine formation, not unaffected, concentrated, or diluted. This underscores PCT's role, critical for filtrate processing, contrasting with later adjustments.

Correct Answer: D

Rationale: Kidneys synthesize calcitriol, secrete erythropoietin, and perform gluconeogenesis all apply. This encompasses metabolic roles, vital for homeostasis, contrasting with single contributions.

Correct Answer: C

Rationale: Renal corpuscle comprises Bowman's capsule and glomerular capillaries, not collecting duct, arteries, or loop. This defines corpuscle, key for filtration, contrasting with tubular parts.