Which of the following best describes the main function of the lungs?

The primary function of the lungs is to facilitate gas exchange, which is crucial for respiration. Within the lungs, there are small air sacs known as alveoli where this exchange occurs. When a person inhales, oxygen from the air fills the alveoli and diffuses into the blood, while carbon dioxide, a byproduct of metabolism, moves from the blood into the alveoli to be exhaled. This efficient transfer of gases is essential for maintaining adequate oxygen levels in the bloodstream and removing carbon dioxide, thereby supporting cellular processes and overall health.

Other functions, such as circulating blood, producing hormones, and digesting food, are performed by different organ systems in the body. The circulatory system is responsible for transporting blood, the endocrine system deals with hormone production, and the digestive system is responsible for food breakdown and nutrient absorption. Thus, while these processes are vital to bodily functions, they are not roles played by the lungs.