The lungs

The lungs are 2 sponge-like organs that are used for breathing. They are part of the respiratory system, which also includes the nose, mouth, trachea (windpipe) and airways (tubes) to each lung. There are large airways known as bronchi (singular: bronchus) and small airways called bronchioles. The lungs sit in the chest and are protected by the rib cage.

Lobes – Each lung is made up of sections called lobes – the left lung has 2 lobes, and the right lung has 3 lobes.

Diaphragm – The lungs rest on the diaphragm, which is a wide, thin muscle that helps with breathing, and separates the chest from the abdomen (belly).

Mediastinum – The space between the lungs is called the mediastinum. A number of important structures lie in this space, including:

• the heart and large blood vessels
• the trachea – the tube that carries air into the lungs
• the oesophagus – the tube that carries food to the stomach
• lymph nodes – small, bean-shaped structures that collect and destroy bacteria and viruses.

Pleura – The lungs are covered by 2 thin layers of tissue called the pleura. The inner layer (visceral pleura) lines the lung surface, and the outer layer (parietal pleura) lines the chest wall, mediastinum and diaphragm. The layers are separated by a small amount of fluid that lets them smoothly slide over each other when you breathe. The pleural cavity is the potential space between the 2 layers; there is no space between the layers when the lungs are healthy.

How breathing works

When you breathe in (inhale), air goes into the nose or mouth, down the trachea and into the bronchi and bronchioles. At the end of the bronchioles, tiny air sacs  called alveoli are surrounded by small blood vessels (capillaries). When the inhaled air reaches the alveoli, oxygen passes into the blood in the capillaries, and waste gas (carbon dioxide) passes out. When you breathe out (exhale), carbon dioxide is removed from the body and released into the air.