Which of these statements is correct?

Correct Answer: D

Rationale: Elastic fibres being more abundant in the bronchi and bronchioles than the upper respiratory tract (choice D) is correct because these structures require elasticity to recoil during expiration, aiding in air movement. Choice A is incorrect as regular (terminal) bronchioles lack glands; glands are found in larger airways like bronchi. Choice B is wrong because the larynx contains cartilage and skeletal muscle, not significant smooth muscle, which is more prominent in the trachea and bronchi. Choice C is false since goblet cells decrease in number in smaller airways like small bronchi and are absent in respiratory bronchioles, which have club cells instead. The abundance of elastic fibres in the lower respiratory tract (bronchi and bronchioles) compared to the upper tract (nasal cavity, pharynx, larynx) supports lung elasticity and function, making D the accurate statement.

Correct Answer: D

Rationale: Emphysema (choice D) increases lung compliance, unlike others, making it the exception. Compliance is ease of lung expansion (ΔV/ΔP). Lung fibrosis (choice A) stiffens tissue, reducing compliance. Increased pulmonary venous pressure (choice B) causes edema, stiffening lungs. Prolonged unventilation (choice C) leads to atelectasis or surfactant loss, decreasing compliance. Alveolar edema (choice E) adds fluid, reducing elasticity. Emphysema destroys alveolar walls, reducing elastic recoil (floppy lungs), increasing compliance despite impaired function. This contrasts with restrictive conditions (A, B, C, E) that stiffen lungs, lowering compliance. Emphysema's obstructive nature raises FRC but eases expansion per pressure unit, distinguishing D as the state not decreasing compliance.

Correct Answer: B

Rationale: the diaphragm moves 7-10 cm during deep breathing, reflecting its maximal excursion. Choice A is true; it rises (relaxes) for expiration, descends (contracts) for inspiration. Choice C is false; contraction varies regionally, though coordinated. Choice D is wrong; internal intercostals aid expiration, not inspiration (external intercostals assist). In deep breathing, the diaphragm flattens significantly, increasing thoracic volume by 5-10 cm, as seen in fluoroscopy. This drives large tidal volumes (e.g., 3-5 L in vital capacity), unlike quiet breathing (1-1.5 cm). As the primary inspiratory muscle, its descent with effort supports B as the accurate statement, consistent with anatomical capacity in healthy adults.

Correct Answer: A

Rationale: substance P, a neuropeptide, causes bronchoconstriction by contracting smooth muscle. Choice B is false; sympathetic discharge (β₂-adrenergic) dilates bronchioles, not constricts. Choice C is wrong; parasympathetic (cholinergic) discharge constricts, not dilates. Choice D is true; bronchoconstriction peaks at 4 am due to circadian vagal tone. Choice E is false; VIP dilates, not constricts. Substance P, released from sensory nerves, mediates inflammation and constriction (e.g., asthma), increasing resistance. This contrasts with autonomic control: sympathetic relaxes, parasympathetic tightens. A's accuracy reflects its role in airway tone regulation.

Correct Answer: D

Rationale: in West's Zone 1 (apex, upright), alveolar pressure (PA) exceeds arterial (Pa) and venous (Pv) pressure, stopping flow. Choice A is false; mean pulmonary artery pressure is ≈15 mmHg, not 25 (systemic range). Choice B is wrong; hypoxia increases pulmonary vascular resistance (vasoconstriction), not decreases. Choice C is true; resistance is lower at total lung capacity (TLC) than functional residual capacity (FRC) due to vessel stretching. Zone 1's high PA (e.g., 0 to +2 cmH₂O) vs. low Pa (e.g., 10 cmH₂O at apex) collapses capillaries, a normal gravitational effect. D accurately reflects this no-flow state.