Which description of alveoli distribution is correct?

The correct description of alveoli distribution is that alveoli are smallest at the base of the lung.

In the anatomy of the lungs, alveoli are tiny air sacs that are crucial for gas exchange. Their size and distribution vary within the lung structure due to differences in pressure and gravitational effects. At the apex of the lung, where the pressure is lower and the alveoli are subject to less compressive force from surrounding tissues, the alveoli tend to be larger. This phenomenon occurs because the alveoli at the apex can expand more freely with less resistance.

Conversely, at the base of the lung, the increased pressure from weight and the surrounding tissues leads to smaller alveoli. The difference in size is significant because it affects how gas exchange takes place in different regions of the lung. Smaller alveoli at the base are more compliant and can facilitate adequate ventilation and perfusion, especially when the individual is upright or in a standing position.

This understanding of alveoli distribution helps in recognizing how the lung's anatomy adapts to physiological requirements, particularly during various activities or body positions.