Which of the following is a cell of the connecting tubules?

Correct Answer: B

Rationale: Principal cells are in connecting tubules (distal/collecting) manage water/Na (e.g., ADH/aldosterone). Intercalated disc is cardiac not renal. Macula densa is distal sensing, not typical connecting. Juxtaglomerular cells are arteriolar renin-focused. Principal cells' presence distinguishes them, key to tubular regulation, unlike misnamed or adjacent cells.

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: A

Rationale: Thirst center activates with 10-15% plasma volume drop or 1-2% osmolarity rise sensitive triggers (e.g., hypothalamus). 1-2% volume or 10-15% osmolarity reverses thresholds incorrect. Thirst is result not stimulus. ADH is parallel not cause. Precise thresholds distinguish it, key to thirst drive, unlike reversed or effect-based options.

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.