Regarding oxygen transport

Correct Answer: B

Rationale: 1 g Hb binds 1.34-1.39 ml O₂ (Hüfner's constant), key to O₂ transport. Choice A is false; only 1-2% of O₂ is dissolved (≈0.3 ml/dL at PaO₂ 100 mmHg), 98% is Hb-bound (≈20 ml/dL). Choice C is wrong; anemia lowers O₂ content, not PaO₂ (dissolved O₂), which remains ≈100 mmHg unless lungs fail. Choice D is false; CO₂ is ≈20 times more soluble than O₂, not 200. Choice E is true; CO₂'s curve is steeper due to solubility, not as steep as O₂'s sigmoid shape (misstated). B reflects Hb's O₂-carrying capacity (e.g., 15 g/dL × 1.34 = 20.1 ml/dL), central to transport physiology, making it the accurate statement.

Correct Answer: D

Rationale: peripheral chemoreceptors (carotid/aortic bodies) increase firing when POâ‚‚ drops below 100 mmHg (e.g., 60 mmHg threshold). Choice A is true; carotid bodies sense all three. Choice B is false; central response to pCOâ‚‚ dominates. Choice C is wrong; aortic bodies are in the arch, not valve. Choice E is false; they sense arterial POâ‚‚. D reflects their hypoxia sensitivity, critical for ventilation drive.

Correct Answer: D

Rationale: functional residual capacity (FRC) is the volume after normal expiration (ERV + RV, ≈2.4 L), not inspiration (FRC + TV = end-inspiratory volume). Choice A is true; tidal volume (TV, ≈500 mL) is normal breathing. ' vital capacity (VC, ≈4.8 L) is max inspiration to max expiration. Choice C is accurate; residual volume (RV, ≈1.2 L) remains after max expiration. FRC, the resting lung volume, balances chest wall and lung recoil, misstated in D as inspiratory, confusing it with inspiratory capacity or end-tidal volume. D's error makes it the incorrect definition.

Correct Answer: D

Rationale: halving radius (r) increases resistance (R) 16-fold per Poiseuille's law (R ∝ 1/r⁴). If r becomes r/2, R = 1/(r/2)⁴ = 16/r⁴. Choice A (2x) is linear. Choice B (4x) is r². Choice C (8x) is r³. Choice E (no effect) ignores physics. In airways (e.g., bronchoconstriction), small changes amplify resistance (e.g., 2 mm to 1 mm, R rises 16x), impacting flow significantly. D reflects this exponential relationship accurately.

Correct Answer: D

Rationale: nose and upper airway receptors respond to mechanical (e.g., flow) and chemical (e.g., irritants) stimuli, triggering sneeze/cough. Choice A (central) is pH-based. Choice B (carotid) and C (aortic) sense blood gases. Choice D (stretch) is mechanical only. Trigeminal/vagal innervation in upper airways detects both types, distinguishing G as the match.