Gaseous exchange takes place in the alveoli and the blood. It refers to the movement of the oxygen and carbon dioxide in and out of the body. It takes place in the lungs through the process of diffusion.
Oxygen and carbon dioxide are exchanged in tiny air sacs called alveoli, which are found at the end of the bronchial tubes of the lungs. Capillaries surround these alveoli. Oxygen moves from the alveoli to the capillaries and enters the bloodstream whenever a person inhales. Simultaneously, carbon dioxide is breathed out of the lungs as a person exhales. This is how gaseous exchange occurs in the alveoli.
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 waste 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 the blood.
Blood capillaries surround the alveoli to ensure adequate blood supply. This is vital as the blood constantly removes oxygen and brings in carbon dioxide to maintain the maximum concentration gradient.
The alveoli have walls that are one cell thick to make the exchange surface extremely thin. This shortens the diffusion distance wherein gases have to move.