Why does the exchange of gases happen only in alveoli, though arteries are present in pharynx, trachea and bronchus ?
Alveoli have several adaptations to maximize the efficiency of gas exchange. They fold to provide a wider surface area for gas exchange to take place and they are ventilated to remove carbon dioxide and to replenish oxygen levels in the alveolar air.
This maintains maximum concentration gradient which refers to the difference in the concentration of a chemical across a membrane, between the air in the alveoli and blood.
The alveoli have thin walls that are one cell thick to make the exchange surface extremely thin.