Which of the following best describes alveoli?

Alveoli are best described as elastic sacs for gas exchange due to their structure and function in the respiratory system. These tiny, balloon-like structures are located at the ends of the bronchial tubes in the lungs and are crucial for the process of respiration. The walls of the alveoli are very thin and are lined with a moist surface that facilitates the diffusion of oxygen and carbon dioxide between the air within the alveoli and the blood in the surrounding capillaries. This gas exchange is essential for supplying oxygen to the bloodstream and removing carbon dioxide from it.

Their elastic nature allows alveoli to expand when inhaling air and to contract during exhalation, helping to maintain the surface area required for efficient gas exchange. This elasticity is vital for maintaining lung function and compliance. Unlike rigid structures, which do not change shape, the ability of alveoli to stretch and rebound enhances their role in breathing. Overall, alveoli play a critical role in the respiratory system, contributing to its primary task of gas exchange, which is fundamental for respiratory health.