Breathing happens in two stages: inhalation and exhalation.

In inhalation, air is breathed in to the lungs. In exhalation, air is released from the lungs. 

When breathing, air travels into our bodies either through the nose or the mouth. From there, the air moves into the trachea, which is located in the throat. The trachea is divided into two bronchial tubes, which transport air to the lungs. The lungs are made of small, ball-shaped pulmonary alveoli.

When the air reaches a pulmonary alveolus, its oxygen is absorbed by the capillary vein of the alveolus. From there, the oxygen continues its journey to the heart and into the rest of the body. 

At the same time as oxygen is absorbed into the capillary veins of the alveoli, harmful carbon dioxide is secreted from other capillary veins into the alveoli. The carbon dioxide is then released from the body during exhalation. 

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