Structure of an Alveolus and its Blood Supply

The alveolus is a minute air sac located at the end of the bronchioles, which are small branches of the bronchus in the lungs.
Each lung contains up to millions of alveoli, providing a vast surface area for gas exchange.
The walls of the alveoli are extremely thin (only one cell thick), which allows for the efficient exchange of oxygen and carbon dioxide.
Surrounding each alveolus is a network of tiny blood vessels, known as capillaries. The walls of these capillaries are also very thin which facilitates rapid gas exchange.
Oxygen diffuses from the air in the alveoli, across the thin walls of the alveoli and capillaries, and into the blood in the capillaries.
Meanwhile, carbon dioxide (a waste product of respiration) diffuses from the blood in the capillaries, across the alveoli and capillary walls, and into the alveoli to be exhaled from the body.
The blood provides the alveoli with a constant supply of oxygen and carbon dioxide. Oxygen-poor, carbon dioxide-rich blood is brought to the alveoli from the body’s tissues, and the oxygen-rich, carbon dioxide-poor blood is taken away from the alveoli to the heart.
This process of gas exchange is facilitated by the fact that the alveoli are moist, which aids in the dissolving of gases.
The inside of the alveoli is coated with a substance called surfactant which reduces the surface tension of water and allows the alveoli to inflate and deflate easily during breathing.
Lastly, alveoli are elastic which allows them to expand and contract as we breathe in and out. This elasticity plays a crucial role in maintaining the flow of air in and out of the lungs.