Mechanism of Ventilation

The mechanism which mammals use to breathe has several parts: lungs, intercostal muscles, a rib cage and a diaphragm - all of which work together to allow breathing to take place. To breathe in, the intercostal muscles expand the rib cage and the diaphragm contracts, moving downwards. These two actions cause the chest cavity containing the lungs to increase in volume. This increase in volume lowers the air pressure inside the lungs and the external air pressure forces air to enter the body.

At rest or during normal daily activity, the external air travels into the body via the nose. Here it is warmed and moistened. From the nose, it travels down the trachaea (windpipe) and into the lungs via the bronchi. Once in the lungs, the air travels through smaller tubes called bronchioles, to reach the alveoli. Alveoli are microscopic air sacs with very thin walls, found within the lungs. They increase the surface area for gaseous exchange. Oxygen diffuses from the air inside the alveoli into the blood and carbon dioxide diffuses out of the blood and into the alveoli. Breathing out (expiration) involves the opposite actions to breathing in (inspiration). The intercostal muscles and diaphragm reduce the volume of the chest (thorax) and the increased pressure causes the air to leave the lungs.

During heavy exercise, the body requires more air than normal. The response is to breathe more heavily and deeply, using the mouth to allow more air into the body. The air breathed in like this isn't warmed or moistened as effectively as breathing through the nose so when exercising in cold weather, the trachaea sometimes hurts. Singers learn to breathe 'from the stomach'. In other words, they use their diaphragm more than normal to help them to breathe in as much air as possible. It is said that this also helps them to control their breathing more precisely, helping them to sing better.

Do you know how oxygen passes into the blood, or what the function of the rib cage is? Try this quiz to see how well you understand the mechanism of ventilation.