Oxygen from the air dissolves into the layer of moisture around each alveoli and moves into minute blood vessels called capillaries.
From here the oxygenated blood is transported back to the heart and pumped round all the organs of the body.
Having delivered its life giving oxygen, the blood returns to the heart rich in carbon dioxide. This carbon dioxide takes the reverse path to the oxygen and is breathed out back into the atmosphere.
It is important for your body to get rid of carbon dioxide which is a waste product of respiration. the lungs help in the elimination of this toxic waste product.