All of the following are criteria of a substance used for GFR measurement, except?

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: Spironolactone (aldosterone inhibitor) decreases K secretion blocks Na reabsorption, reducing K exchange (e.g., collecting duct). High plasma K increases secretion stimulates. Proximal diuretic (e.g., acetazolamide) raises distal K increases. Alkalosis boosts K secretion H /K shift. Aldosterone block distinguishes it, key to K sparing, unlike secretion-enhancing factors.

Correct Answer: C

Rationale: Angiotensin II receptors are in the zona glomerulosa stimulate aldosterone release (e.g., adrenal cortex). Juxtaglomerular cells produce renin not receptors. Macula densa senses lacks these. Intercalated cells manage pH not angiotensin. Adrenal location distinguishes it, key to RAAS, unlike renal or tubular sites.

Correct Answer: C

Rationale: The bicarbonate buffer system is most important rapidly neutralizes H (e.g., CO₂/HCO₃⁻ in blood). Bone buffers chronically slow. Phosphate is secondary intracellular/tubular. Proteins assist less capacity. Bicarbonate's speed distinguishes it, key to acute pH control, unlike slow or secondary systems.

Correct Answer: B

Rationale: At 5000 m, hypoxia drives hyperventilation PCOâ‚‚ falls (COâ‚‚ blown off), pH rises (respiratory alkalosis). Both lower misstates pH rises. Both higher ignores altitude false. pH fall/PCOâ‚‚ rise is hypoventilation opposite. Alkalotic shift distinguishes it, key to high-altitude response, unlike uniform or reversed changes.