A 12 years-old boy has a severe asthmatic attack with wheezing. His arterial pO2 is 60 mmHg and pCO2 is 30 mmHg. His:

Correct Answer: D

Rationale: In a severe asthma attack, bronchoconstriction obstructs airways, reducing airflow, especially on expiration, causing wheezing. FEV1/FVC decreases (<80%) as FEV1 drops more than FVC due to obstruction, not increases. The ventilation/perfusion (V/Q) ratio in affected areas falls, as ventilation is blocked while perfusion persists, causing hypoxemia (PaO2 60 mmHg vs. 75-100 mmHg normal). Arterial PCO2 (30 mmHg vs. 35-45 mmHg) is lower, not higher, because hypoxemia stimulates hyperventilation via peripheral chemoreceptors, expelling CO2 faster than it builds up, a compensatory response in acute asthma. Inadequate gas exchange lowers PaO2, not PCO2, here. Option D correctly ties low PCO2 to hyperventilation driven by hypoxia, aligning with asthma's physiology where obstruction impairs oxygen uptake but CO2 clearance accelerates with increased respiratory effort.

Correct Answer: C

Rationale: Lung compliance (C = ΔV / ΔP) measures volume change per pressure unit, correctly defined. It's not maximal during quiet breathing (VT ~500 ml) compliance peaks at moderate volumes, declining near TLC due to stiffness, making that false but not the exception here. The statement more surface tension, more compliance' is incorrect high tension (e.g., no surfactant) reduces compliance by stiffening alveoli, per Laplace's law (P = 2T/r), as in RDS, while low tension increases it. Fibrosis decreases compliance via collagen stiffening true. Emphysema (not listed) raises compliance by elasticity loss. The surface tension error contradicts physiology compliance falls with rising tension, making it the exception, as surfactant's role is to enhance compliance by reducing tension, critical for understanding lung mechanics.

Correct Answer: D

Rationale: Pulmonary function tests (PFTs) differ by disease. Obstructive (e.g., COPD) reduces airflow, lowering FEV1 (<80% predicted) from airway narrowing, with increased residual volume (RV) and total lung capacity (TLC). Restrictive (e.g., fibrosis) limits expansion, also reducing FEV1 due to less volume, with decreased RV and TLC. Decreased FEV1 fits both obstructive from obstruction, restrictive from capacity loss. Decreased RV is restrictive-only (obstructive increases RV). Normal or above TLC fits obstructive (restrictive lowers it). Vascular resistance (not a PFT) rises in fibrosis, not decreases. Decreased FEV1's commonality reflects exhalation impairment across types, making it the shared value, critical for broad PFT interpretation.

Correct Answer: C

Rationale: The greenhouse effect occurs when greenhouse gases (e.g., CO2, CH4, H2O) absorb and re-emit infrared radiation from Earth's surface, trapping heat in the atmosphere. Ozone absorbs UV (~200-310 nm), protecting life, not driving greenhouse warming false. Cloud reflection (albedo ~0.3) cools by deflecting solar radiation, not trapping heat false. Conduction transfers heat to air, but radiation dominates atmospheric retention false. Absorption/re-emission of infrared (~4-100 μm) by gases increases atmospheric temperature (e.g., ~33°C warmer than without), per radiative forcing models (e.g., IPCC), making it the primary process, central to climate dynamics.

Correct Answer: D

Rationale: Pseudostratified ciliated columnar epithelium lines much of the respiratory tract, aiding mucus movement. The infraepiglottis (A) and vestibular fold (B) in the larynx, and conducting bronchioles (C) in the lungs, feature this epithelium with cilia and goblet cells for mucus clearance. The superior nasal cavity (D), or olfactory region, differs it's lined with olfactory epithelium, a specialized pseudostratified epithelium with olfactory receptor cells, sustentacular cells, and basal cells, lacking cilia and goblet cells, optimized for smell, not mucus transport. Though pseudostratified, its distinct function and structure (non-ciliated) exclude it from the typical respiratory lining described, making D the exception.