The diaphragm:

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: 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.

Correct Answer: D

Rationale: joint and muscle receptors (mechanoreceptors) drive early exercise hyperpnea via proprioceptive feedback to the medulla. Choice A (central) responds to COâ‚‚/pH later. Choice B (carotid) and C (aortic) sense hypoxia/COâ‚‚, secondary in normoxia. Choice D (stretch) modulates pattern. Muscle spindles and tendon organs signal effort within seconds, initiating ventilation rise before chemical changes, making H key in exercise onset.

Correct Answer: A

Rationale: no consistent evidence shows males eliminate carboxyhemoglobin (COHb) faster than females elimination depends on Oâ‚‚ partial pressure and ventilation. Choice B is true; ambient air compresses, but Oâ‚‚ is 100%. ' dissolved Oâ‚‚ rises (e.g., 6 mL/100 mL at 3 atm). Choice D is accurate; therapy uses 2-3 atm. Choice E (toxicity) is plausible. Hyperbaric Oâ‚‚ accelerates COHb clearance equally by POâ‚‚, not sex, making A the false claim.