Final answer:
Alveoli are crucial structures in the lungs that facilitate gas exchange, with each lung containing about 300 million alveoli to provide a large surface area for oxygen and carbon dioxide to diffuse between the bloodstream and the air within the lungs.
Step-by-step explanation:
Alveoli are thin-walled chambers in the lungs, surfaces for gas exchange, clusters at the end of each bronchiole, and are surrounded by a network of capillaries. Each one of the alveoli is approximately 200 to 300 microns in diameter and is a component of the alveolar sacs, with each sac containing 20 to 30 alveoli. These tiny air sacs are the functional units where oxygen and carbon dioxide are exchanged between the air we breathe and the bloodstream. The large number of alveoli, about 300 million per lung, provides a surface area of approximately 75 m², which is essential for efficient gas exchange. This exchange is made possible by the thin-walled nature of the alveolar cells and their direct contact with the capillaries.