Diffusion is inversely proportional to:

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: 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.

Correct Answer: B

Rationale: the lung converts angiotensin I to II (AII) via ACE but doesn't metabolize AII degradation occurs elsewhere (e.g., liver). Choice A is true (ACE activity). Choice C is correct (bradykinin inactivation). Choice D is accurate (serotonin uptake). Choice E (arachidonic acid) occurs via cyclooxygenase. The lung's ACE role is synthetic, not catabolic for AII, making B the exception.

Correct Answer: D

Rationale: total lung capacity (TLC) = vital capacity (VC) + residual volume (RV), e.g., 4.8 + 1.2 = 6 L in men. Choice A (VC + TV) overcounts inspiratory volume. Choice B (VC + FRC) double-counts RV and ERV. Choice C (TV + RV) is too small (≈1.7 L). TLC encompasses all lung volume (RV + ERV + TV + IRV), and VC (ERV + TV + IRV) plus RV completes it. E aligns with standard lung volume definitions.