Inside the alveoli, oxygen moves across the paper-thin walls to the capillaries, the tiny blood vessels, and then into the blood, where it is picked up by chemicals, haemoglobin, in the red blood cells ready to be carried throughout the body (Way pp). At the same time, waste products from the body, in the form of carbon dioxide, come out of the capillaries back into the alveoli, ready to be breathed out (Way pp). Freshly oxygenated blood is carried from the lungs to the left side of the heart which pumps blood around the body through the arteries, and once the oxygen is used up, the blood returns, through the veins, to the right side of the heart (Way pp). From there, it is pumped to the lungs so that the carbon dioxide can be removed and more oxygen taken in (Way pp). Every day, some 10,000 liters of air move in and out of the lungs, carrying germs and other foreign bodies as well as oxygen (Way pp). Thus,...

Tiny hairs line the bronchi and help waft unwanted materials up to the mouth (Way pp). Mucus produced in the walls of the airways helps to keep them clean and well lubricated, and cells in the lungs contain enzymes that produce chemical changes in the blood (Way pp).
The delicate structure of the lungs is perfectly adapted to carry out the complex job of breathing and, al the same time, aids in protecting the body from outside attack (Way pp). Yet, the lungs can be damaged, for example, by cigarette smoke, air pollution, and occupational gases and dusts (Way pp). Damage to the lungs can lead to breathlessness and disease (Way pp).

Works Cited

The Way Our Lungs Work. British Lung Foundation. http://www.lunguk.org/the-way-our-lungs-work.asp