The lungs are organs of the respiratory system contained within the chest cavity. There are two lungs, one on the left side of the chest and one on the right side. The right lung is divided into three sections, known as lobes, whilst the left is separated into two. Each lung is encased by a two-layered membrane, also known as pleura, which attach the lungs to the chest cavity.
Air goes in to the lungs via the trachea (windpipe), this divides into a series of branching airways called bronchi, and the air then travels from the bronchi into millions of tiny air sacs (alveoli).
Oxygen from the air is then passed into the bloodstream through the walls of the alveoli and transported around the body.
During this process Carbon dioxide is produced and in turn expelled from the body through exhalation.