Concerning the pulmonary circulation in a normal man:

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: 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.

Correct Answer: A

Rationale: physiological dead space (anatomic + alveolar) equals anatomical dead space (≈150 mL) in healthy lungs at rest alveolar dead space is negligible. Choice B is true; base ventilates more (gravity). Choice C is correct (7 mL/kg, ≈500 mL for 70 kg). Choice D is accurate; resistance drops with volume (airway stretch). Choice E (20x increase) is true. Normal Vₓ/Vₜ (0.3) matches anatomic dead space, making A's ‘larger' claim false.