What are the microscopic air sacs in the lungs called?

The microscopic air sacs in the lungs are known as alveoli. These structures are crucial for the respiratory system as they are the primary site of gas exchange. Each alveolus is surrounded by a network of capillaries, which allows oxygen from the air to diffuse into the blood while carbon dioxide is expelled from the blood into the air within the alveoli to be exhaled.

Alveoli are designed to maximize surface area, facilitating efficient gas exchange. They are incredibly numerous, with millions present in the lungs, further contributing to their ability to oxygenate blood effectively. This structure enhances the overall respiratory process, making alveoli essential for breathing and oxygenating the body.

The other options, while related to the respiratory system, refer to different structures. Bronchi are the larger passageways that lead to the lungs, trachea is the windpipe that connects the throat to the bronchi, and capillaries are tiny blood vessels that are involved in nutrient and gas exchange but are not the air sacs themselves.