alveolae

Alveoli are tiny, balloon-like air sacs found in the lungs. They are the primary sites of gas exchange in the respiratory system, where oxygen from inhaled air passes into the bloodstream and carbon dioxide from the blood is transferred to the air to be exhaled.

These microscopic structures are clustered together in grapelike formations at the end of the bronchioles, which are small airways within the lungs. Each lung contains millions of alveoli, providing a vast surface area for efficient gas diffusion. The walls of the alveoli are extremely thin, typically only one cell thick, and are surrounded by a dense network of tiny blood vessels called capillaries. This close proximity between the air in the alveoli and the blood in the capillaries facilitates the rapid movement of gases.

The process of gas exchange at the alveolar level is driven by differences in partial pressures. Oxygen has a higher partial pressure in the alveolar air than in the blood arriving from the body, causing it to diffuse into the capillaries. Conversely, carbon dioxide has a higher partial pressure in the capillary blood than in the alveolar air, prompting its diffusion into the alveoli to be expelled. This critical function of the alveoli is essential for sustaining life by ensuring the body receives a constant supply of oxygen and removes waste carbon dioxide.