What are the tiny air sacs in the lungs where gas exchange occurs called?

The tiny air sacs in the lungs where gas exchange occurs are called alveoli. These structures play a crucial role in the respiratory system by facilitating the exchange of oxygen and carbon dioxide between the air we breathe and the bloodstream. Each alveolus is surrounded by a network of capillaries, allowing oxygen to diffuse into the blood and carbon dioxide to be expelled from the blood into the alveoli for exhalation.

The design of alveoli, being small and numerous, greatly increases the surface area available for gas exchange, making the process efficient and effective. Their thin walls, comprised of a single layer of epithelial cells, further enhance this gas exchange due to the short diffusion distance for gases.

In contrast, bronchi are the larger air passages that branch off from the trachea and lead to the lungs, lobules refer to subdivisions of the lungs that contain multiple alveoli, and pleurisy is an inflammation of the pleura, which are the membranes surrounding the lungs, but does not refer to any structure involved in gas exchange. Each of these options represents different aspects of lung anatomy and function but do not describe the primary sites of gas exchange themselves.