Where is resistance highest in the respiratory system?

• A. Small airways
• B. Large airways
• C. Alveoli
• D. Bronchioles

Answer: (B)

The resistance in the respiratory system is highest in the large airways. This is primarily because the large airways, which include the trachea and main bronchi, have a larger diameter compared to smaller airways. Although larger airways may seem to provide lower resistance due to their width, they exhibit higher overall resistance due to their structural complexity and the presence of various muscular and connective tissues that can constrict or limit airflow.

In addition, the large airways are responsible for conducting a substantial volume of air and have a significant impact on overall airway resistance. The phenomenon of turbulence in these larger passages further contributes to resistance when airflow is increased, such as during exercise.

In contrast, smaller airways, including the bronchioles, have a greater cumulative cross-sectional area, which leads to lower resistance overall, despite their smaller individual diameter. Alveoli, being the sites of gas exchange, do not contribute significantly to airway resistance. Hence, when considering where resistance is highest in the respiratory system, large airways are the primary contributors due to their structure and the dynamics of airflow they facilitate.