You are up very high where barometric pressure is 447 mmHg. What is the partial pressure of oxygen in the air up there?

Correct Answer: C

Rationale: At 447 mmHg barometric pressure, inspired pO₂ = FiO₂ × (P_atm - PH₂O). Assuming 37°C, PH₂O = 47 mmHg, FiO₂ = 0.21: pO₂ = 0.21 × (447 - 47) = 0.21 × 400 = 84 mmHg. Choice C (60 mmHg) is closest, possibly reflecting a simplified estimate or slight variation (e.g., dry air miscalculation). Choice A (0.5 mmHg) is absurdly low; B (40 mmHg) fits alveolar pO₂ at sea level; D (120 mmHg) exceeds sea-level inspired (≈150 mmHg); E (150 mmHg) is sea-level normal. At altitude, lower P_atm reduces pO₂, triggering acclimatization. 60 mmHg approximates high-altitude inspired air (e.g., 10,000 ft), making C reasonable despite exactness to 84 mmHg.

Correct Answer: C

Rationale: diffusing capacity (DₗO₂) increases ≈3-fold (25 to 65-75 ml/min/mmHg) in exercise via recruitment and perfusion. Choice A is false; VO₂ is ≈3-4 L/min in fit subjects, not 6 L/min (elite athletes). Choice B is wrong; RER rises above 1.0 (e.g., 1.2), not to 0.8. ' cardiac output rises less than ventilation (e.g., 4x vs. 20x), but not a sixth. Choice E is false; the curve shifts right. C reflects enhanced O₂ uptake capacity, critical for exercise, making it true.

Correct Answer: C

Rationale: anatomical dead space, the volume of conducting airways (nose to terminal bronchioles), is ≈150 mL in a healthy adult (≈2 mL/kg, e.g., 75 kg). Choice A (50 mL) is too low, underestimating airway volume. Choice B (100 mL) is insufficient for typical adults. Choice D (200 mL) slightly overestimates, though it's closer in larger individuals. Anatomical dead space, measured via Fowler's method (N₂ washout), excludes alveoli and reflects non-gas-exchanging regions. It's roughly one-third of tidal volume (500 mL), consistent across healthy subjects, varying with body size. C aligns with standard physiology texts (e.g., 150-160 mL), making it the accurate value.

Correct Answer: C

Rationale: surface tension is the force along a liquid surface (e.g., alveoli), reducing area. Choice A is false; deflation volume exceeds inflation (hysteresis) due to surfactant. Choice B is wrong; compliance is ΔV/ΔP, not area (that's work). ' alveolar pressure is 2T/R (one surface), not 4T/R (soap bubble). Choice E is false; surfactant is from Type II cells, not I. C defines surface tension's role in Laplace's law, critical for alveolar stability.

Correct Answer: D

Rationale: pulmonary stretch receptors initiate the Hering-Breuer reflex, inhibiting inspiration during lung inflation. Choice A (central) controls chemically. Choice B (carotid) and C (aortic) sense blood gases. Stretch receptors, in bronchial smooth muscle, signal via vagus, preventing overinflation (e.g., prolonged expiration at high volumes), making D the accurate initiator.