Alveoli: The Tiny Air Sacs Essential for Gas Exchange

Alveoli are microscopic, balloon-like air sacs located at the end of the bronchial tree in the lungs. They are the primary site of gas exchange, where oxygen from inhaled air diffuses into the bloodstream and carbon dioxide—a waste product of metabolism—diffuses from the blood into the alveoli to be exhaled.

Structure and Function

Each alveolus is surrounded by a dense network of capillaries. The walls of both the alveoli and capillaries are extremely thin (only one cell thick), allowing for efficient diffusion of gases. The inner surface of the alveoli is coated with surfactant, a substance that reduces surface tension and prevents the sacs from collapsing during exhalation.

Key Points

• Gas Exchange: Oxygen enters the blood; carbon dioxide leaves.
• Surface Area: The human lungs contain approximately 300–500 million alveoli, providing a massive surface area (about 70–100 square meters) for gas exchange.
• Capillary Network: Pulmonary capillaries envelop each alveolus, ensuring close contact between air and blood.

Healthy alveolar function is critical for maintaining adequate oxygen levels in the body and removing carbon dioxide efficiently.