alveooli

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 released into the lungs to be exhaled.

Each lung contains millions of alveoli, collectively providing a vast surface area for efficient gas transfer. The walls of alveoli are extremely thin, typically only one cell layer thick, which minimizes the distance for gases to travel. They are also surrounded by a dense network of capillaries, the smallest blood vessels, ensuring close contact between the air in the alveoli and the blood.

A thin layer of moisture lines the inner surface of each alveolus, which helps gases dissolve before diffusion. Surfactant, a substance produced by specialized cells within the alveolar walls, reduces the surface tension of this fluid. This prevents the alveoli from collapsing during exhalation and makes breathing easier.

The structure of alveoli is crucial for respiration. Their large collective surface area, thin walls, and rich capillary supply are all adaptations that maximize the uptake of oxygen and the removal of carbon dioxide, supporting the metabolic needs of the body.