All of the following shift the Hb dissociation curve to the right during exercise EXCEPT:

Correct Answer: D

Rationale: decreased pO₂ doesn't shift the Hb dissociation curve right it's a condition, not a modifier. Choices A (2,3-DPG), B (pCO₂), and C (temperature) shift it right, reducing Hb-O₂ affinity (Bohr effect), enhancing O₂ unloading in exercise. 2,3-DPG rises in active tissues, stabilizing deoxy-Hb. Elevated pCO₂ and H⁺ (CO₂ hydration) and heat (muscle work) favor release. Low pO₂ moves along the curve (P₅₀ = 26 mmHg), not shifting it affinity stays unless pH, CO₂, or temperature change. Exercise boosts O₂ delivery; right shifts (P₅₀ to ≈30 mmHg) aid this, while pO₂ reflects demand, not curve position. D is the exception.

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.

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.