How do I breathe?

When you breathe, you draw air in through the nose and mouth and into the lungs. Air consists of 79 percent nitrogen and about 21 percent oxygen, with small amounts of carbon dioxide and other, rare gases. Air travels down a tube called the trachea that forks into other tubes called bronchi, which lead into the lungs. From here the air passes into a series of smaller air passages and eventually into tiny air sacs, or bladders, called alveoli. Oxygen is absorbed through the thin walls of the alveoli into the blood, and waste carbon dioxide is released to be breathed out as a waste product.

 

 

 

 

 

 

 

 

 

 

How big are the alveoli?

Each alveolus is about 0.2 mm across. The walls of the alveoli are very thin — only one cell thick — so oxygen and carbon dioxide can easily pass through. There are probably 300 million alveoli in the lungs.