The kidneys maintain acid-base balance by mainly

Correct Answer: B

Rationale: Kidneys maintain acid-base balance by excreting H and reabsorbing HCO₃⁻ e.g., PCT reclaims HCO₃⁻, distal tubule secretes H . Excreting both loses buffer acidosis risk. Reabsorbing H /excreting HCO₃⁻ reverses alkalosis. Reabsorbing both retains acid imbalanced. H excretion/HCO₃⁻ retention distinguishes it, key to pH regulation, unlike dual loss or retention.

Correct Answer: C

Rationale: Filtration based on blood pressure occurs at the glomerulus hydrostatic pressure (~55 mmHg) drives GFR (e.g., renal corpuscle). Collecting duct reabsorbs not filters. Distal tubule adjusts post-filtration. Loop concentrates not pressure-driven. Glomerulus's pressure filtration distinguishes it, key to urine initiation, unlike tubular roles.

Correct Answer: D

Rationale: Most body water (~60%) is in cells intracellular fluid (e.g., ~40 L in 70 kg adult). Plasma is ~3 L small fraction. Lymph is minimal circulatory subset. Tissue fluid (interstitial) is ~15% less than cells. Cellular dominance distinguishes it, critical for hydration, unlike extracellular options.

Correct Answer: D

Rationale: Sodium is the best osmolarity indicator dominant extracellular ion (~140 mM, e.g., drives osmosis). Calcium is minor (~2.5 mM) less impact. Chlorine follows Na secondary. Potassium is intracellular not plasma. Na 's prevalence distinguishes it, critical for osmolarity, unlike lesser ions.

Correct Answer: C

Rationale: pH above 7.4 is alkalosis base excess (e.g., HCO₃⁻ rise). Acidosis is below 7.35 acidic. Diuresis is urine output not pH. Natriuresis is Na excretion unrelated. Alkalosis's high pH distinguishes it, critical for acid-base status, unlike low pH or unrelated terms.