The purpose of respiration is to supply the body with oxygen and eliminate carbon dioxide. Oxygen is essential for cellular respiration as cells cannot exist in the absence of it.
The human lungs are the organs responsible for respiration. Together with the nasal cavity, pharynx, larynx and trachea, they form the respiratory system. When a person inhales, air flows through the airways, inflating the lungs and filling them with oxygen. When a person exhales, the air from lungs flows out of the airways. The same cycle repeats with every single breath. As many other functions of the body, respiration is controlled by the autonomic nervous system.