Final answer:
The small saccular outpocketings in the lungs that are essential for gas exchange are called alveoli. These are part of alveolar sacs, with roughly 300 million alveoli per lung contributing to a large surface area equivalent to a tennis court.
Step-by-step explanation:
The small saccular outpocketings within the lungs that provide surfaces for the diffusion of gases are known as alveoli. Alveoli are tiny, thin-walled structures, approximately 200 to 300 microns in diameter, found within alveolar sacs at the ends of alveolar ducts.
Each alveolar sac contains around 20 to 30 alveoli, which are in direct contact with the capillaries of the circulatory system. This intricate arrangement facilitates the efficient exchange of oxygen and carbon dioxide between the blood and the lungs.
With roughly 300 million alveoli per lung, they provide a large surface area for gas exchange, comparable to the size of a tennis court, approximately 75 m². This extensive surface area is crucial for effectively allowing oxygen to diffuse into the blood, while carbon dioxide diffuses out of the blood into the alveoli to be exhaled.