Regarding bronchial asthma, all the following statements are true EXCEPT?

Correct Answer: A

Rationale: Bronchial asthma involves reversible airway obstruction from inflammation, bronchoconstriction, and mucus. Airway resistance increases due to narrowed bronchi, reducing airflow. During an attack, FEV1/FVC drops below 80% (e.g., 50-60%) as FEV1 falls more than FVC, reflecting obstruction. Bronchodilators (e.g., albuterol) are standard treatment, relaxing smooth muscle to relieve constriction. Allergies (e.g., pollen) often trigger attacks, a common feature. However, cough suppressants aren't highly indicated asthma's productive cough clears mucus, and suppressing it worsens obstruction and infection risk. Therapy focuses on bronchodilation and inflammation control (e.g., corticosteroids), not cough suppression, which could exacerbate symptoms. This statement contradicts asthma management principles, making it the exception among true descriptions of the condition's pathophysiology and treatment.

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: B

Rationale: CO2 percentage correlates with PCO2, highest where metabolic CO2 accumulates. Pulmonary arteries carry deoxygenated blood from the right heart to lungs, with PCO2 ~45-46 mmHg venous blood richest in CO2 from tissues, topping the list. Alveolar air equilibrates with arterial blood at ~40 mmHg during gas exchange. Pulmonary veins, post-exchange, carry oxygenated blood with PCO2 ~40 mmHg, arterial levels. Interstitial fluid's PCO2 (~45 mmHg or less) mirrors venous blood or local metabolism but isn't a standard respiratory metric. Systemic arteries (not listed) are also ~40 mmHg. Pulmonary arteries, transporting CO2-rich blood for exhalation, have the highest PCO2, reflecting their pre-exchange role, distinguishing them from oxygenated or equilibrating sites in the respiratory cycle.

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.