What is the primary function of the alveoli in the lungs?

The primary function of the alveoli in the lungs is to exchange gases with the pulmonary capillaries. Alveoli are tiny, balloon-like structures where the exchange of oxygen and carbon dioxide occurs between the air we breathe and the bloodstream. When oxygen enters the alveoli, it diffuses across the thin alveolar walls and into the surrounding capillaries, where it binds to hemoglobin in red blood cells. Concurrently, carbon dioxide produced by the body's metabolism travels from the blood into the alveoli to be exhaled. This essential process enables the body to deliver oxygen to tissues and remove carbon dioxide, which is vital for maintaining proper physiological functions.

The other options address functions that are not the primary role of the alveoli. For instance, filtering particles from the air is primarily handled by structures such as the nose and cilia in the respiratory tract. The production of mucus is a function of mucus-secreting cells in the respiratory system, which helps trap particles and pathogens. Regulation of blood pressure is primarily managed by the cardiovascular system and involves mechanisms in the heart and blood vessels, not the alveoli. Thus, the correct answer highlights the alveoli's key role in gas exchange.