Alveoli

Alveoli are tiny air sacs surrounded by many blood capillaries.

It is important that gas exchange takes place efficiently.

Oxygen had to diffuse through the lining of the alveolus and through the capillary wall.

Carbon dioxide has to diffuse in the opposite direction.

Each alveolus is surrounded by a network of blood capillaries.

This increases the efficiency of absorption.

The wall of each alveolus is only one cell thick, this increases the efficiency of absorption.