The major functions of the respiratory system are:

1. Gas exchange: the respiratory system allows oxygen in the air to enter the blood and carbon dioxide to leave the blood and enter the air. The cardiovascular system transports oxygen from the lungs to the cells of the body and carbon dioxide from the cells of the body to the lungs.

2. Regulation of blood pH, which can be altered by changes in blood carbon dioxide levels.

3. Voice production as air moves past the vocal cords to make sound and speech.

4. Olfaction, or the sense of smell, occurs when airborne molecules are drawn into the nasal cavity.

5. Innate immunity, providing protection against some microorganisms by preventing their entry into the body or by removing them from respiratory surfaces.