Mean pressure (mmHg) in the main pulmonary artery is:

Correct Answer: D

Rationale: mean pulmonary artery pressure (mPAP) is ≈15 mmHg in a healthy adult (systolic ≈25, diastolic ≈8). Choice A (2 mmHg) is far too low, below venous levels. Choice B (5 mmHg) underestimates pulmonary circulation. Choice C (8 mmHg) is diastolic, not mean. Choice E (25 mmHg) is systolic, not mean. mPAP reflects low-resistance pulmonary flow (≈1/10 systemic), driven by right ventricular output. Catheterization data confirm 15 mmHg as normal, distinguishing it from systemic pressures (≈100 mmHg mean), making D the precise value.

Correct Answer: D

Rationale: FEV₁ is ≈80% of FVC in healthy adults (FEV₁/FVC ratio ≈ 0.75-0.85). Choice A (50%) suggests obstruction (e.g., COPD). Choice B (60%) and C (70%) are low for normals. Choice E (90%) is high, nearing restriction. FEV₁ (forced expiratory volume in 1 s) reflects airway patency; FVC (forced vital capacity) is total expirable volume. A ratio of 80% indicates normal flow, making D standard.

Correct Answer: A

Rationale: Bohr's method calculates physiological dead space (VD = VT · (PaCO₂ - PECO₂) / PaCO₂), not anatomic (Fowler's N₂ washout does). Choice B is true (≈150 mL). ' deep breaths stretch airways. Choice D is accurate (≈2 mL/kg). Choice E (conducting zone) is true. A's methodological error makes it the exception.

Correct Answer: C

Rationale: perfusion decreases more than ventilation from base to apex (gravity), making V/Q higher at apex (e.g., 3 vs. 0.6 at base). Choice A is true (apex V/Q ≈ 3). Choice B is correct (third rib ≈ 1). Choice D is accurate (whole lung ≈ 0.8). Choice E (exercise increases) is true. Ventilation gradient is less steep (4:1 base-to-apex) than perfusion (10:1), reversing C's claim, making it false.

Correct Answer: B

Rationale: serotonin (5-HT) is not synthesized by the lung it's produced by enterochromaffin cells and neurons, then removed by pulmonary endothelium (monoamine oxidase). Choice A (prostaglandins) is synthesized (e.g., PGIâ‚‚ by endothelium). Choice C (DPPC) is made by Type II pneumocytes (surfactant). Choice D (histamine) is produced by mast cells. Choice E (kallikrein) is lung-derived. The lung metabolizes serotonin but lacks tryptophan hydroxylase for synthesis, distinguishing B as the non-synthesized substance.