Where are most micro-villi found?

Correct Answer: D

Rationale: Microvilli maximize surface area in the PCT for reabsorption, not loop or DCT (fewer). This specifies absorptive structure, key for efficiency, contrasting with minimal presence elsewhere.

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: B

Rationale: Micturition reflex integrates in the sacral spinal cord (S2-S4), not medulla (respiration), hypothalamus (hormones), or lumbar (lower). This locates reflex center, key for bladder control, contrasting with higher regions.

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.