At high altitudes all of the following things occur in an effort to acclimatise EXCEPT

Correct Answer: A

Rationale: Hypoventilation (choice A) doesn't occur at high altitudes; it's the exception. Low pOâ‚‚ triggers hyperventilation via peripheral chemoreceptors, increasing ventilation to raise PaOâ‚‚. Polycythemia (choice B) increases RBCs/Hb, boosting Oâ‚‚ capacity after days. Capillary density rises (choice C) in tissues, enhancing Oâ‚‚ delivery over weeks. The Oâ‚‚ dissociation curve shifts right (choice D) due to increased 2,3-DPG, aiding Oâ‚‚ unloading despite lower PaOâ‚‚. Pulmonary vasoconstriction (choice E) occurs acutely, shunting blood to better-ventilated areas. Hypoventilation would worsen hypoxemia, countering acclimatization's goal of optimizing Oâ‚‚ availability. Hyperventilation lowers PaCOâ‚‚, causing alkalosis (later compensated renally), making A the process that doesn't aid high-altitude adaptation.

Correct Answer: C

Rationale: the Bohr effect shifts the O₂ dissociation curve right due to pCO₂ increasing H⁺, reducing Hb affinity. Choice A is false; left shift increases affinity. Choice B is wrong; decreased 2,3-DPG shifts left, not right. ' temperature shifts the curve (right with increase). Choice E is false; 2,3-DPG rises at altitude. The Bohr effect, driven by CO₂'s pH impact, aids O₂ unloading in tissues (P₅₀ rises), a key adaptation. C accurately describes this mechanism.

Correct Answer: D

Rationale: Choice D is correct (replacing E); helium (low density) reduces turbulence (lower Reynolds number, Re = ρvD/μ). Choice A is false; large airways (higher velocity) are more turbulent than small (laminar). Choice B is wrong; turbulent flow scales less than linearly with pressure (not doubled). ' turbulence depends on density, not viscosity (laminar does). Low-density gases decrease Re, easing flow in obstructive disease, making D true.

Correct Answer: D

Rationale: the chloride shift moves HCO₃⁻ out of the RBC (not in) and Cl⁻ in, maintaining neutrality as CO₂ forms HCO₃⁻. Choice A is true (Fick's law: V ∝ A/T). Choice B is correct (Bohr effect: PCO₂ → H⁺ → right shift). Choice C is accurate (Henry's law). Choice E is true (Haldane effect). D reverses ion directions; HCO₃⁻ exits via band 3 exchanger, Cl⁻ enters, supporting CO₂ transport, making it the error.

Correct Answer: B

Rationale: carotid bodies contain glomus cells Type I (dopamine-rich, neurotransmitter) and Type II (support) sensing POâ‚‚, PCOâ‚‚, pH. Choice A (central) lacks glomus cells. Choice C (aortic) has similar cells but is less prominent. Choice D (stretch) is mechanical. Carotid bodies, at carotid bifurcations, use Type I cells to signal hypoxia, releasing dopamine, making B the precise match.