The Respiratory System

The cells of the body get the energy they need by combining digested food with oxygen brought to them by the blood. This process is called tissue respiration. It produces water and carbon dioxide. As blood passes through the lungs, it absorbs fresh supplies of oxygen from the air, and releases the unwanted carbon dioxide which is carried away from the cells


Our lungs are two spongy bags of tissue filled with millions of tiny air spaces called alveoli. These have very thin walls and are surrounded by a dense network of fine blood tubes called capillaries.

Oxygen from the air that you breathe passes through the thin walls into the blood; at the same time, the unwanted carbon dioxide passes out of the blood into the air spaces so the lungs can breathe it out into the atmosphere.

As you breathe, air moves in and out of the lungs through the windpipe and some of the old air in the air spaces is exchanged for new air. Our lungs hang in an airtight space called the thorax.


When you breathe IN, two things happen at once; the diaphragm muscles pull the diaphragm downwards and the muscles between the ribs pull the ribcage upwards and outwards. These muscle movements increase the size of the thorax, and the lungs expand as air flows in to fill up the extra space.

When you breathe OUT, the diaphragm muscles and the muscles between the ribs relax, the thorax returns to its original size and air is pushed out of the lungs.

During light breathing, the breathing action is mainly produced by movement of the diaphragm muscles.

The muscles between the ribs are used when greater amounts of air are moved in and out of the lungs - during running for example. With more air flowing into the  and out of the lungs, the blood can absorb oxygen and release carbon dioxide at faster rates.

Exercise is good for us as it makes us breathe in more oxygen which our exercising muscles need to keep them healthy.