Regarding surfactant:

Correct Answer: C

Rationale: surfactant's phospholipid film forms via tubular myelin, a precursor from Type II pneumocytes. Choice A is false; phospholipids (e.g., DPPC) treat IRDS but need proteins (SP-B, SP-C) for full efficacy. Choice B is wrong; smoking reduces surfactant via oxidative damage. Choice D is true; IRDS results from surfactant deficiency, increasing tension and collapsing alveoli. Choice E is false; carbohydrates aid stability, but phospholipids dominate. Tubular myelin, rich in dipalmitoylphosphatidylcholine, reduces surface tension (Laplace's law: P = 2T/r), stabilizing alveoli. C accurately describes this process, critical for lung function.

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.

Correct Answer: D

Rationale: ventral respiratory group (VRG) neurons include expiratory cells that discharge spontaneously in forced breathing, not silent as stated. Choice A is true; centers and chemoreceptors are distinct. ' quiet expiration is passive (recoil). Choice C is accurate; inspiratory neurons (DRG) drive phrenic nerves. Choice E (12-15/min) fits. VRG's role in active expiration contradicts D's ‘no discharge,' making it false.