The Law of Laplace implies that:

Correct Answer: D

Rationale: in a blood vessel, P = T/R (Laplace for cylinders), unlike alveoli (P = 2T/R). Choice A is false; alveoli use P = 2T/R (sphere with one surface). Choice B is wrong; soap bubbles (two surfaces) use P = 4T/R. Choice C is true but not the law's direct statement surfactant prevents this. Laplace relates pressure, tension, and radius; vessels (tubular) differ from spherical alveoli. D accurately applies this to vascular physiology.

Correct Answer: D

Rationale: irritant receptors, between epithelial cells, adapt rapidly to mechanical/chemical stimuli (e.g., dust, smoke), triggering cough/bronchoconstriction. Choice A (central) is chemical, not airway-based. Choice B (carotid) and C (aortic) are vascular. Choice D (stretch) adapts slowly. Irritant receptors, vagally mediated, protect airways with quick responses, distinguishing E as the correct type.

Correct Answer: C

Rationale: lower regions (base) ventilate better than upper (apex) due to gravity and compliance gradients. Choice A is true (TV ≈ 500 mL). Choice B is correct (dead space ≈ 150-160 mL). Choice D is accurate (Bohr's method). Choice E (none) is false. Base ventilation exceeds apex (e.g., 4:1 ratio upright), reflecting diaphragm motion and pleural pressure, making C the error.

Correct Answer: D

Rationale: increased carboxyhemoglobin (COHb) shifts the curve left, not right, by enhancing Hb-O₂ affinity (CO binds 240x stronger). Choice A (temperature), B (PCO₂), and C (H⁺) shift it right via the Bohr effect, aiding O₂ unloading (P₅₀ up, e.g., 26 to 30 mmHg). Choice D (DPG) also shifts right. COHb reduces available Hb, left-shifting the curve for remaining O₂, impairing tissue delivery (e.g., in poisoning), opposite to exercise adaptations. E's distinct effect makes it the exception.

Correct Answer: C

Rationale: arterial blood carries only ≈5-7% of CO₂ in dissolved form (≈0.3 mL/100 mL at PaCO₂ 40 mmHg), not 20% total CO₂ is ≈48-50 mL/100 mL, mostly as HCO₃⁻ (70-80%) and carbamino compounds (10-20%). Choice A is true; O₂ solubility (0.003 mL/mmHg/100 mL) is ≈20x less than CO₂ (0.06). ' deoxygenation enhances CO₂ binding (Haldane effect) via deoxy-Hb's higher affinity. Choice D is plausible; venous hematocrit may rise slightly due to plasma shifts, though minimal in normals. Dissolved CO₂ contributes a small fraction, and C's overestimate contradicts standard physiology (e.g., 20% would imply 10 mL/100 mL, far exceeding solubility), making it the false statement.