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

Correct Answer: B

Rationale: Principal cells are found in the collecting tubules (or ducts), where they regulate water and sodium balance via ADH and aldosterone. ‘Connecting tubules' likely refers to the collecting system in this context. Intercalated discs are cardiac structures, macula densa is in the distal tubule, and juxtaglomerular cells are in arterioles, making B the correct answer.

Correct Answer: C

Rationale: Increased alveolar ventilation expels more CO₂, reducing blood PCO₂. Per the Henderson-Hasselbalch equation (pH = 6.1 + log([HCO₃⁻]/[0.03 × PCO₂])), lower PCO₂ increases pH (respiratory alkalosis) and decreases extracellular H⁺ concentration, as H⁺ binds with HCO₃⁻. Options A, B, and D misalign with this, making C correct.

Correct Answer: C

Rationale: Isolation reduces sensory input, and in an 80-year-old, this sensory deprivation (C) can cause confusion, hallucinations, and reduced comprehension, especially with limited stimulation. Fluid/electrolyte imbalance (A) lacks supporting data (e.g., labs), a stimulating environment (B) contradicts isolation, and sundowning (D) ties to evening confusion, not isolation, making C the likely cause.

Correct Answer: C

Rationale: During the resting (filling) stage of micturition, the detrusor muscle, a smooth muscle in the bladder wall, contracts minimally and stretches to accommodate urine (C), maintaining continence with sphincter tone. Urination (A) and sphincter relaxation (B) occur during voiding, and control (D) is broader, making C correct.

Correct Answer: D

Rationale: Mesangial cells contract to reduce filtration area (A), not produce systemic angiotensin II (B, a juxtaglomerular cell role), and phagocytose debris (C). A and C are true—contraction adjusts GFR, phagocytosis clears mesangium—while B is false, making D (A and C are correct) the answer.