Which statement about the alveolar region contributes to rapid absorption of inhaled drugs?

• A. It has a thin membrane separating alveoli from circulation
• B. It has a low surface area
• C. It actively metabolizes most inhaled drugs
• D. It has a thick barrier and low blood flow

Answer: (A)

Rapid uptake of inhaled drugs hinges on diffusion across a very thin barrier between the air in the alveoli and the blood in the pulmonary capillaries. This minimal diffusion distance, along with the alveoli’s large surface area and rich blood supply, lets drugs cross into systemic circulation quickly. The statement that the alveolar region has a thin membrane separating alveoli from circulation directly reflects this fast diffusion pathway, making it the best explanation for rapid absorption.

If the surface area were low, absorption would be slower because there would be less area for diffusion. Alveoli do not actively metabolize most inhaled drugs to a degree that dominates absorption, and a thick barrier with low blood flow would hinder diffusion rather than promote it.