Regarding airway resistance

Correct Answer: C

Rationale: decreased alveolar pCO₂ (e.g., hyperventilation) causes bronchodilation via chemoreceptor feedback, reducing airway resistance, not increasing it. Choice A is false; Poiseuille's law (R = 8ηL/πr⁴) applies to laminar flow, not turbulent. Choice B is wrong; medium-sized bronchi, not smallest bronchioles, contribute most resistance due to cumulative cross-sectional area changes. ' as lung volume drops, resistance rises bronchioles narrow without radial traction. Choice E (adrenergic contraction increasing resistance) is false; adrenergic stimulation relaxes bronchial muscle, lowering resistance. Low pCO₂ signals reduced CO₂ clearance need, relaxing airways to adjust ventilation, opposite to bronchoconstriction (e.g., high pCO₂). This physiological response makes C the true statement about resistance dynamics.

Correct Answer: D

Rationale: Choice D is not true; inspiratory capacity (IC) in men is ≈3.3 L (TV + IRV, 0.5 + 2.8 L), not 4.8 L. ' FRC (≈2.4 L) equals ERV (≈1 L) + RV (≈1.4 L). Choice B is true; IRV is ≈3.3 L in men. Choice C is accurate; RV in women is ≈1.1 L. Choice E is correct; TLC is ≈6 L (men), 4.2 L (women). IC reflects maximal inspiratory volume from FRC; 4.8 L exceeds typical male values (closer to vital capacity). Standard lung volumes (e.g., 70 kg male) confirm D's overestimation, making it the false statement.

Correct Answer: D

Rationale: mixed venous PO₂ (PvO₂) is ≈50 mmHg on 100% O₂. With FiO₂ = 1.0, PaO₂ rises to ≈650 mmHg (PIO₂ = 760 - 47 ≈ 713 mmHg, minus A-a gradient). O₂ content increases (dissolved O₂ ≈ 2 ml/100 ml + Hb-bound), but tissues extract ≈5 ml/100 ml O₂, dropping PvO₂ to 50-55 mmHg (SaO₂ near 100%). Choice A (40 mmHg) is normal air breathing. Choice B (713 mmHg) is arterial, not venous. Choice C (650 mmHg) overestimates venous saturation. D reflects the balance of high arterial O₂ and tissue uptake.

Correct Answer: A

Rationale: RQ nears 1.0 in exercise (e.g., 0.8 to 1.2) as metabolism shifts. Choice B is true but incomplete; PIO₂ = FiO₂ · (PB - PH₂O). Choice C is false; PACO₂ ≈ PaCO₂ (≈40 mmHg) in normals. Choice D is wrong; PAO₂ ≈ 100 mmHg (150 - 40/0.8), not 150. Exercise increases VCO₂ relative to VO₂, raising RQ, especially anaerobically. The equation (PAO₂ = PIO₂ - PACO₂/RQ) adjusts dynamically, making A the accurate statement.

Correct Answer: A

Rationale: central chemoreceptors (medulla) dominate minute-by-minute ventilation, sensing CSF pH (CO₂-driven, 70-80% of response). Choice B (carotid) and C (aortic) contribute <20% (O₂, CO₂, pH), critical in hypoxia. Choice D (stretch) fine-tunes via Hering-Breuer reflex. Central receptors adjust breathing rate/depth to maintain PaCO₂ ≈ 40 mmHg, responding within seconds to CO₂ shifts, making A the primary controller.