An 80-year-old patient is placed in isolation when infected with methicillin-resistant Staphylococcus aureus. The patient was alert and oriented on admission, but is now having visual hallucinations and can follow only simple directions. The medical-surgical nurse recognizes that the changes in the patient's mental status are related to:

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: 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.

Correct Answer: D

Rationale: Using Henderson-Hasselbalch: pH = 6.1 + log([HCO₃⁻]/(0.03 × pCO₂)), 7.60 = 6.1 + log([HCO₃⁻]/(0.03 × 40)). Solving: 1.5 = log([HCO₃⁻]/1.2), 10^1.5 = [HCO₃⁻]/1.2, 31.6 ≈ [HCO₃⁻]/1.2, [HCO₃⁻] ≈ 40 mEq/L. D (40) matches, indicating alkalosis.

Correct Answer: C

Rationale: Aldosterone (C) increases sodium reabsorption and potassium secretion in the distal tubule, regulating electrolytes. Renin (A) triggers the RAAS, angiotensin II (B) stimulates aldosterone, and angiotensin I (D) is a precursor, making C the direct effector.

Correct Answer: A

Rationale: Higher GFR (A) increases filtrate volume, reducing PCT reabsorption time, raising Na⁺ concentration reaching the DCT. Decrease (B) or no change (C) assumes full compensation, but faster flow elevates Na⁺, making A correct.