With respect to regional gas exchange in the upright lung

Correct Answer: C

Rationale: In the upright lung, the ventilation/perfusion (V̇/Q̇) ratio is highest at the apex (choice C), due to gravity's effect. Ventilation is greater at the base (choice A is false), as dependent alveoli expand more. Perfusion is also greater at the base (choice B is false), with blood flow higher in lower zones (e.g., 4:1 base-to-apex ratio). V̇/Q̇ at the apex (≈3) exceeds the ideal 0.8, being ‘abnormally high' relative to perfect matching, while the base is ≈0.6. PO₂ is highest at the apex (choice D is false), as high V̇/Q̇ over-ventilates relative to perfusion; bases have lower PO₂ due to lower V̇/Q̇. pH follows PO₂ trends, not bases (choice E false). C's high V̇/Q̇ reflects physiological mismatch, driving regional gas exchange differences.

Correct Answer: D

Rationale: diffusion is inversely proportional to the square root of molecular weight (Graham's law), though less dominant in lungs. Choice A is false; diffusion is proportional to the diffusion constant (Fick's law: V = D·A·ΔP/T). Choice B is wrong; it's proportional to area. ' it's proportional to solubility. Choice E is false; it's proportional to partial pressure difference. In lungs, solubility and gradient drive O₂/CO₂ diffusion, but molecular weight (√MW) affects gas speed in free states. D's inverse relationship holds in diffusion theory, making it correct.

Correct Answer: D

Rationale: RQ = 1.0 for carbohydrate metabolism (VCOâ‚‚ = VOâ‚‚). Choice A is true; high V/Q (apex) lowers RQ (less COâ‚‚ relative to Oâ‚‚). Choice B is false; base RQ is lower (higher perfusion). Choice C is wrong; RQ = VCOâ‚‚ / VOâ‚‚, not reverse. D reflects metabolic stoichiometry, a standard definition.

Correct Answer: C

Rationale: PCO₂ = 600 mmHg (extreme hypercapnia) with HCO₃⁻ = 28 mEq/L (near normal) indicates acute respiratory acidosis. Using Henderson-Hasselbalch (pH = 6.1 + log(HCO₃⁻ / (0.03 · PCO₂))), pH ≈ 6.1 + log(28 / 18) ≈ 6.3, severely acidic due to high PCO₂. Choice A (metabolic) requires low HCO₃⁻. Choice B needs higher HCO₃⁻ (e.g., 40). Choice D implies compensation (HCO₃⁻ rise, e.g., 40-50), not seen here. Choice E (alkalosis) contradicts PCO₂. Acute hypoventilation (e.g., obstruction) causes this uncompensated state, making C accurate.

Correct Answer: C

Rationale: aortic bodies respond to POâ‚‚ and PCOâ‚‚ but are less sensitive to pH than carotid bodies (which sense all three). Choice A (central) detects pH via COâ‚‚. Choice B (carotid) includes pH sensitivity. Choice D (stretch) is mechanical. Aortic bodies, in the aortic arch, prioritize gas tensions, with pH a secondary signal via carotid dominance, making C the best fit.