Regarding bronchial tone:

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: 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.

Correct Answer: C

Rationale: carotid bodies markedly increase firing when arterial PO₂ falls below 60 mmHg, not 70 mmHg, which is a less pronounced threshold. Choice A is true; central chemoreceptors reside in the medulla, sensing CSF pH. ' hypoxia (via peripheral chemoreceptors) enhances CO₂ sensitivity, amplifying ventilation. Choice D is accurate; carotid bodies have exceptionally high blood flow (≈2000 mL/min/100 g) for rapid gas sensing. Choice E (CO₂ dominance) is also true. The carotid bodies' steep response curve begins at ≈60 mmHg, driving significant respiratory stimulation below this level (e.g., SaO₂ < 90%), as seen in hypoxia studies. At 70 mmHg, stimulation is milder, making C's threshold overstated and thus the incorrect statement.