First, air is breathed or inspired into the lungs
The air moves into the small air spaces called alveoli, which is where gas exchange occurs.
The alveoli are in direct contact with capillaries.
Inspired air has a higher concentration of oxygen than the capillaries and a lower concentration of carbon dioxide.
The two gasses move by diffusion (from an area of higher to lower concentration).
Therefore, the oxygen moves to the capillaries and the carbon dioxide moves to the alveoli.
Then, carbon dioxide is exhaled. Oxygenated blood is carried to the heart and then the rest of the body.
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