What is the site of gas exchange in the lung between the atmosphere and the blood?

The alveoli are the specific structures in the lungs where gas exchange occurs between the atmosphere and the blood. These tiny, balloon-like sacs are surrounded by a mesh of capillaries. This design maximizes the surface area available for the exchange of oxygen and carbon dioxide.

When air enters the lungs through the trachea and bronchi, it eventually reaches the alveoli. Here, oxygen from the inhaled air diffuses across the alveolar walls into the blood, while carbon dioxide in the blood diffuses into the alveoli to be exhaled. This efficient exchange is critical for maintaining the body’s oxygen levels and removing carbon dioxide, a waste product of metabolism.

Other structures like the bronchi, bronchioles, and trachea are part of the airway passage that conducts air to and from the alveoli but do not participate directly in the gas exchange process. They provide the route for airflow but are not involved in the diffusion of gases into or out of the bloodstream.