Hypoxia at high altitudes:

Correct Answer: B

Rationale: high-altitude hypoxia (hypoxemic, low pO₂) causes cyanosis (bluish skin) as Hb saturation drops (e.g., PaO₂ ≈ 60-70 mmHg at 3,000 m). Choice A is false; stagnant hypoxia involves low flow, not low FiO₂ (altitude). Choice C is wrong; 3,000 m causes mild symptoms (e.g., headache) in unacclimatized people, not severe (e.g., edema, >4,000 m). ' 100% O₂ corrects PaO₂ but not acclimatization deficits (e.g., alkalosis). Cyanosis (>5 g/dL deoxy-Hb) is visible when SaO₂ falls (e.g., 85%), a hallmark of altitude hypoxia, making B the accurate statement.

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.

Correct Answer: C

Rationale: acclimatization shifts the Oâ‚‚ curve right (increased 2,3-DPG), not left. Choice A is true; Oâ‚‚ toxicity (e.g., >1 atm) causes seizures. ' hyperoxia damages infant retinas. Choice D is accurate; polycythemia boosts Oâ‚‚ capacity. Choice E (mountain sickness) fits hypoxemia/alkalosis. Right shift aids Oâ‚‚ unloading at altitude, making C the error.