What primarily regulates resistance in the airways?

• A. Diameter of bronchioles
• B. Length of the alveoli
• C. Surface tension of fluids
• D. Airway temperature

Answer: (A)

The primary factor that regulates resistance in the airways is the diameter of the bronchioles. As the diameter of these small air passages changes, it significantly impacts the resistance to airflow. When bronchioles constrict, the airway diameter decreases, leading to an increase in resistance and consequently a reduction in airflow to the lungs. Conversely, when bronchioles dilate, the resistance decreases, allowing for greater airflow.

Other factors, such as the length of alveoli, surface tension of fluids, and airway temperature do play roles in the respiratory system, but they do not have as direct or significant an effect on airway resistance as the diameter of bronchioles does. The length of alveoli primarily relates to surface area for gas exchange rather than airflow resistance, surface tension is important for maintaining the stability of the alveoli but does not directly impact the resistance of airflow through the bronchioles, and while temperature can influence respiratory dynamics, it does not serve as a primary regulator of airway resistance.