Which of the following is false about sodium reabsorption?

Correct Answer: B

Rationale: Sodium entering the tubule at the luminal membrane is false enters cell from lumen, exits to blood (e.g., PCT). Early reabsorption is true ~65%. Na /K -ATPase drives active exit passive misstated but mechanism holds. All correct overstates entry error. Direction distinguishes the falsehood, key to Na transport, unlike location or pump truths.

Correct Answer: C

Rationale: With ADH, water reabsorption in collecting duct is passive osmosis via aquaporins (e.g., medullary gradient). Active transport is Na not water. Cortical-only mislimits medullary too. All passive distinguishes it, key to ADH's osmotic drive, unlike active or partial errors.

Correct Answer: D

Rationale: Bone buffers in chronic metabolic acidosis releases CaCO₃ (e.g., weeks-long compensation). Phosphate is tubular less chronic. Proteins assist limited capacity. Bicarbonate depletes overwhelmed. Bone's role distinguishes it, key to chronic buffering, unlike acute or depleted systems.

Correct Answer: C

Rationale: Simultaneous respiratory (PCO₂ 68, high) and metabolic acidosis (HCO₃⁻ 13, low) match pH 6.90 severe drop (e.g., overdose hypoventilation, lactic acidosis). Uncompensated metabolic lacks PCO₂ rise partial. Uncompensated respiratory misses HCO₃⁻ drop sole. Renal compensation raises HCO₃⁻ not here. Dual acidosis distinguishes it, key to mixed disorder, unlike single or compensated states.

Correct Answer: A

Rationale: Urine forms via filtration (glomerulus), reabsorption (tubules), and secretion (tubules) not digestive or GI processes. This outlines nephron function, critical for waste removal, contrasting with unrelated mechanisms.