All of these statements about surfactant are true except

Correct Answer: C

Rationale: Choice C is false. Surfactant, produced by Type II pneumocytes (choice E), reduces surface tension (choice B) and stabilizes alveoli (choice A) by equalizing pressure across sizes, preventing collapse. It also lowers alveolar pressure, reducing fluid transudation into capillaries (choice D). However, per Laplace's law (P = 2T/r), surface tension (T) drives pressure (P) inversely with radius (r). Without surfactant, smaller alveoli would have higher pressure and collapse into larger ones (higher T, lower r). Surfactant lowers T more in smaller alveoli, equalizing pressure, not making larger alveoli's T lower than smaller ones' it balances them. Choice C misstates this; larger alveoli naturally have lower pressure due to larger r, but T isn't inherently lower without surfactant's effect. Thus, C contradicts surfactant's role, making it the false statement.

Correct Answer: B

Rationale: the diaphragm moves 7-10 cm during deep breathing, reflecting its maximal excursion. Choice A is true; it rises (relaxes) for expiration, descends (contracts) for inspiration. Choice C is false; contraction varies regionally, though coordinated. Choice D is wrong; internal intercostals aid expiration, not inspiration (external intercostals assist). In deep breathing, the diaphragm flattens significantly, increasing thoracic volume by 5-10 cm, as seen in fluoroscopy. This drives large tidal volumes (e.g., 3-5 L in vital capacity), unlike quiet breathing (1-1.5 cm). As the primary inspiratory muscle, its descent with effort supports B as the accurate statement, consistent with anatomical capacity in healthy adults.

Correct Answer: A

Rationale: substance P, a neuropeptide, causes bronchoconstriction by contracting smooth muscle. Choice B is false; sympathetic discharge (β₂-adrenergic) dilates bronchioles, not constricts. Choice C is wrong; parasympathetic (cholinergic) discharge constricts, not dilates. Choice D is true; bronchoconstriction peaks at 4 am due to circadian vagal tone. Choice E is false; VIP dilates, not constricts. Substance P, released from sensory nerves, mediates inflammation and constriction (e.g., asthma), increasing resistance. This contrasts with autonomic control: sympathetic relaxes, parasympathetic tightens. A's accuracy reflects its role in airway tone regulation.

Correct Answer: D

Rationale: in West's Zone 1 (apex, upright), alveolar pressure (PA) exceeds arterial (Pa) and venous (Pv) pressure, stopping flow. Choice A is false; mean pulmonary artery pressure is ≈15 mmHg, not 25 (systemic range). Choice B is wrong; hypoxia increases pulmonary vascular resistance (vasoconstriction), not decreases. Choice C is true; resistance is lower at total lung capacity (TLC) than functional residual capacity (FRC) due to vessel stretching. Zone 1's high PA (e.g., 0 to +2 cmH₂O) vs. low Pa (e.g., 10 cmH₂O at apex) collapses capillaries, a normal gravitational effect. D accurately reflects this no-flow state.

Correct Answer: D

Rationale: vasopressin (ADH) passes through the lungs unchanged. Choice A (serotonin) is inactivated by monoamine oxidase. Choice B (bradykinin) is broken down by ACE. Choice C (leukotrienes) are metabolized or excreted. Choice D (prostaglandin Eâ‚‚) is inactivated by pulmonary enzymes. The lung's endothelium clears amines, peptides, and eicosanoids, but vasopressin, a systemic hormone, resists metabolism, maintaining its antidiuretic role. E's inert passage aligns with pulmonary metabolic selectivity.