The primary purpose of inhaling is to bring oxygen into the lungs so that it can be transferred to the blood through the alveoli, enabling gas exchange. This oxygen is then transported by the circulatory system to body tissues where it is used for cellular respiration, a process that produces energy for the cells. Inhalation refreshes the air in the alveoli, maintaining the partial pressures of oxygen and carbon dioxide in the blood and supporting homeostasis of blood pH

. In more detail, during inhalation, the diaphragm contracts and moves downward, and the muscles between the ribs contract to expand the chest cavity. This expansion lowers the pressure in the lungs, causing air rich in oxygen to flow in through the nose or mouth, down the airways, and into the alveoli. Oxygen then diffuses across the alveolar walls into the blood capillaries, while carbon dioxide from the blood diffuses into the alveoli to be exhaled later

. Thus, inhaling primarily serves to supply oxygen necessary for cellular metabolism and to facilitate the removal of carbon dioxide, a metabolic waste product