The lungs are located in the chest (thoracic cavity) and are part of the respiratory system.
Structure
The lungs take up most of the space inside the chest. They are separated by the heart and mediastinum and are enclosed by the chest wall (made up of the thoracic ribs and intercostal muscles) and the diaphragm.
The lungs and inner wall of the chest are covered by a thin membrane called the pleura. The pleura is made up of two layers:
- inner (visceral) layer, also called the visceral pleura – the layer next to the lung
- outer (parietal) layer, also called the parietal pleura – the layer that lines the chest wall
The area between the two layers is called the pleural space.
Each lung is divided into lobes (sections):
- The left lung has two lobes.
- The right lung has three lobes and is slightly larger than the left lung.
The trachea (windpipe) divides into two tubes called the main bronchi. One bronchus goes to each lung. The main bronchi divide into smaller bronchi (which have small glands and cartilage in their walls) and eventually into small tubes called bronchioles (which have no glands or cartilage). At the end of the bronchioles are millions of tiny sacs called alveoli.
Function
The main function of the lungs is to transfer oxygen from the air to the blood and release carbon dioxide from the blood to the air.
The pleura helps protect and cushion the lungs. It produces a lubricating fluid that allows the two layers of the pleura to slide easily over each other so the lungs can move smoothly in the chest during breathing.
Air enters the mouth or nose and travels through the trachea (windpipe), bronchi and bronchioles to the alveoli. The exchange of oxygen and carbon dioxide takes place in the alveoli:
- The oxygen is absorbed from the air in the alveoli and passes into the blood to be circulated around the body.
- The carbon dioxide, which is a waste product of the body's cells, passes from the blood into the alveoli and is breathed out.