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While children do have higher metabolic rates and oxygen demands, this is not the main reason for the exaggerated effect of inflammation on airway resistance.

The cartilaginous and flexible trachea in infants contributes to collapsibility but does not explain the disproportionate rise in resistance from swelling.

Greater diaphragmatic reliance affects breathing mechanics but not the mathematical relationship between airway narrowing and resistance.

While moisture in the alveoli facilitates gas exchange, this is not the main role of the mucociliary clearance system, alveolar moisture regulation is handled by surfactant and fluid balance mechanisms, not cilia and mucus.

Adaptive immunity involves lymphocytes and antigen-specific responses, which are separate from the mechanical clearance provided by the mucociliary system.

Angiotensin-converting enzyme (ACE) production occurs mainly in the pulmonary capillary endothelium, not as part of mucociliary clearance.

Alveolar macrophages are part of the innate immune system, not adaptive immunity. They engulf and destroy pathogens and debris but do not produce specific antibodies.

Infants’ cough and sneeze reflexes are actually less forceful and less coordinated than adults’, making clearance of secretions less efficient.

Secretory Immunoglobulin A (sIgA) is part of the active mucosal immune system, not passive immunity. Passive immunity is typically acquired via maternal antibodies (e.g., IgG via placenta, IgA via breast milk).

Sternocleidomastoid muscles are accessory muscles used during respiratory distress, not for quiet breathing in healthy infants.

Intercostal muscles are not fully developed in newborns and provide minimal contribution to chest wall stability or ventilation.

Abdominal muscles assist in forced exhalation and coughing but are not the primary drivers of quiet respiration.

Tonsils in children tend to be relatively large, not small, and can contribute to obstruction. The nasal passages are narrow, but this option misses the critical role of cricoid cartilage development.

The child’s larynx is funnel-shaped, not cylindrical, with the narrowest point at the cricoid cartilage. While sinuses develop over time, their underdevelopment doesn’t directly increase risk of upper airway obstruction.

Children actually have proportionally larger tongues relative to their oral cavity, which can contribute to obstruction, so “smaller tongue” is inaccurate.

A: This represents suprasternal retractions, typically seen at the sternal notch with upper-airway obstruction (e.g., croup, laryngomalacia). Not “substernal.”

B: The xiphoid itself is the bony tip; retractions are named for the soft tissue below it (subxiphoid/substernal). At the xiphisternum isn’t the same as below the sternum.

C: Those are intercostal retractions along the lateral chest wall, not beneath the sternum.