Regarding the lung

Questions 71

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Question 1 of 5

Regarding the lung

Correct Answer: D

Rationale: All statements are true (choice D replaced with E). Choice A: 300 million alveoli is accurate, enabling vast gas exchange surface (≈70 m²). Choice B: Terminal bronchioles are the smallest conducting airways, lacking alveoli; respiratory bronchioles follow with alveoli. Choice C: Anatomic dead space ≈ 150 ml in adults, reflecting conducting airway volume. Choice D: Alveoli average 0.2-0.3 mm diameter, supporting diffusion efficiency. No statement is false; ‘all true' applies. The lung's design numerous alveoli, structured airways, and dead space optimizes ventilation and perfusion. Misinterpreting terminal bronchioles as alveolar might confuse, but they're correctly described. Thus, D (E) is correct as all hold physiologically.

Question 2 of 5

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.

Question 3 of 5

In exercise:

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.

Question 4 of 5

The volume of the anatomical dead space is:

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.

Question 5 of 5

Regarding the elastic properties of the lung:

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.

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