The largest cross-sectional area and therefore lower resistance of airways?

Correct Answer: B

Rationale: Airway resistance follows Poiseuille's law (R ∝ 1/r^4), but total cross-sectional area governs overall resistance. The trachea, a single tube (~2 cm diameter), has ~3-4 cm² area. Bronchioles, numbering thousands, reach ~300 cm² collectively at terminal stages, yet pale beside alveoli. Alveoli (~300 million) total ~70-100 m² (~700,000-1,000,000 cm²) during inspiration, dwarfing other structures. This vast area slows airflow velocity, reducing resistance to negligible levels at the gas exchange site, where diffusion dominates. Resistance peaks in medium bronchi due to turbulent flow, not alveoli, despite their tiny individual size (~0.2 mm). Trachea and bronchioles handle bulk flow with higher resistance. Alveoli's massive area minimizes resistance, making them the correct choice, critical for efficient ventilation and distinguishing their role from conducting airways.

Correct Answer: C

Rationale: Functional residual capacity (FRC, ~2.5-3 L) is the lung volume post-normal expiration, a resting state where lung inward recoil balances chest wall outward recoil true for both lung and thorax, but not the focus. The true statement is that at FRC, intra-alveolar pressure equals atmospheric pressure (~760 mmHg), as no airflow occurs (gradient = 0), with muscles relaxed. Intrapleural pressure (IPP) is negative (~-4 mmHg, 756 mmHg) at FRC, not above atmospheric (760 mmHg), maintaining lung expansion false if elevated. Compliance isn't lowest at FRC (not listed). Alveolar-atmospheric equality is a core principle, ensuring rest stability, making it the standout truth, reflecting FRC's role as the ventilatory baseline.

Correct Answer: A

Rationale: Airway resistance (R ∝ 1/r^4) peaks in large airways (trachea, bronchi), where turbulent flow dominates (~80% of R), despite smaller radii in later generations (bronchioles). Their vast number increases cross-sectional area (~300 cm² vs. 3-4 cm²), reducing total R distally false. Normally, R is highest in large airways true. Increased R (e.g., asthma) lowers FEV1/FVC (<70%) true. Loss of elasticity (emphysema) and bronchoconstriction (asthma) raise R true. The false claim of increasing R in later generations misreads branching dynamics resistance drops as area rises, making large airways the primary site, aligning with airflow physiology.

Correct Answer: A

Rationale: The troposphere, extending ~0-12 km above Earth's surface, contains ~80% of atmospheric mass and nearly all weather phenomena clouds, rain, storms driven by solar heating, convection, and water vapor. The stratosphere (~12-50 km) holds the ozone layer, stable and dry, with minimal weather. The mesosphere (~50-85 km) is cold, with rare noctilucent clouds, not typical weather. The thermosphere (~85-600 km) is thin, hot from solar radiation, and weatherless. The troposphere's density and dynamics (e.g., Hadley cells) foster weather, per meteorological data (e.g., AMS), making it the key layer, distinct from higher, less active regions.

Correct Answer: C

Rationale: The lateral nasal wall's blood supply (A) includes the sphenopalatine (external carotid) and anterior ethmoidal (internal carotid) arteries, making A true. Innervation (B) via ophthalmic (V1) and maxillary (V2) branches of the trigeminal nerve is correct. Lymphatic drainage (D) to submandibular and retropharyngeal nodes aligns with nasal anatomy. However, venous drainage (C) primarily goes to the facial vein and pterygoid plexus, not mainly to the cavernous sinus via a large emissary vein that's more relevant to the dangerous triangle of the face or specific infections. Small connections exist via ethmoidal veins, but C overstates this route, making it the least accurate.