What is the primary function of alveoli in the lungs?

The primary function of alveoli in the lungs is to facilitate the exchange of gases. Alveoli are tiny air sacs located at the end of the respiratory tree where the exchange of oxygen and carbon dioxide occurs. Their structure is ideally suited for this function, as they provide a large surface area and are surrounded by a network of capillaries, allowing for efficient gas diffusion.

As air enters the lungs, oxygen from the air diffuses through the thin walls of the alveoli into the blood in the capillaries, while carbon dioxide in the blood diffuses from the capillaries into the alveoli to be exhaled. This gas exchange is crucial for respiration, as it provides oxygen to the body for cellular processes and removes carbon dioxide, a waste product of metabolism.

Other options are unrelated to the respiratory function of alveoli. The transportation of blood back to the heart is carried out by the circulatory system, not the alveoli. The absorption of nutrients from digested food takes place in the intestines, and producing digestive enzymes is a function of the digestive organs, such as the pancreas and salivary glands. Therefore, facilitating the exchange of gases is the specific and essential role of alveoli in the respiratory system.