Alveolar ventilation in a male with a respiratory rate of 10/min and tidal volume of 600 ml is

Correct Answer: D

Rationale: Alveolar ventilation (V̇A) = (tidal volume - dead space) × respiratory rate. With TV = 600 ml, dead space ≈ 150 ml, and rate = 10/min, V̇A = (600 - 150) × 10 = 4500 ml/min (choice D). Choice A (1000 ml) fits a lower TV or rate (e.g., 250 ml × 4). Choice B (1750 ml) suggests miscalculation (e.g., 325 ml × 5). Choice C (3000 ml) aligns with TV = 450 ml at 10/min. Choice E (6000 ml) ignores dead space (600 × 10). Dead space (150 ml) is air not reaching alveoli; only 450 ml/breath ventilates gas exchange zones. At 10 breaths, 4500 ml/min reflects effective CO₂ removal and O₂ uptake, matching physiological norms for a resting adult, confirming D.

Correct Answer: D

Rationale: Choice D is correct (replacing E); normal P₅₀ is ≈26-27 mmHg, the pO₂ at 50% Hb saturation. Choice A is false; HbS has valine replacing glutamic acid (β6 mutation). Choice B is wrong; saturation is the percentage of sites with O₂, not without. ' oxygenated Hb is the R (relaxed) state, not T (tense). Choice E (27 mmHg) is true but redundant here. P₅₀ reflects Hb-O₂ affinity; 27 mmHg is standard at pH 7.4, 37°C, aligning with physiological O₂ unloading. D's accuracy makes it the correct statement.

Correct Answer: D

Rationale: in a blood vessel, P = T/R (Laplace for cylinders), unlike alveoli (P = 2T/R). Choice A is false; alveoli use P = 2T/R (sphere with one surface). Choice B is wrong; soap bubbles (two surfaces) use P = 4T/R. Choice C is true but not the law's direct statement surfactant prevents this. Laplace relates pressure, tension, and radius; vessels (tubular) differ from spherical alveoli. D accurately applies this to vascular physiology.

Correct Answer: B

Rationale: 2,3-DPG levels rise at altitude (hypoxia response), shifting the curve right. Choice A is true; PCO₂ shifts it right (Bohr effect). Choice C is false; deoxy-Hb is tense (T state), not relaxed (R state). Choice D is wrong; CO's affinity is ≈240x, shifting left by reducing available Hb, not curve shape. Altitude adaptation increases 2,3-DPG, aiding O₂ unloading (P₅₀ up), making B the accurate chronic response.

Correct Answer: D

Rationale: irritant receptors, between epithelial cells, adapt rapidly to mechanical/chemical stimuli (e.g., dust, smoke), triggering cough/bronchoconstriction. Choice A (central) is chemical, not airway-based. Choice B (carotid) and C (aortic) are vascular. Choice D (stretch) adapts slowly. Irritant receptors, vagally mediated, protect airways with quick responses, distinguishing E as the correct type.