How you breathe

About 20,000 breaths a day. Meet the muscles, tubes and air sacs that make each one happen.

5 minutes · 6 stops

In through the windpipe
Air enters through your nose or mouth and flows down the trachea, the windpipe. Rings of cartilage keep it open. You can feel them as gentle ridges in the middle of your lower neck.
Branching into the lungs
Behind your breastbone the windpipe splits into two bronchi, one for each lung. They keep branching into smaller and smaller tubes, like an upside-down tree, ending in tiny air sacs.
A tennis court of air sacs
Your lungs contain hundreds of millions of air sacs wrapped in tiny blood vessels. Spread out, they would cover roughly a tennis court. Oxygen crosses into your blood here, and carbon dioxide crosses out.
The muscle that does the work
Most breathing is done by the diaphragm, a dome of muscle under your lungs. When it contracts it flattens, making space for the lungs to fill. Hiccups are sudden spasms of this muscle.
Helpers between the ribs
Muscles between your ribs lift the ribcage up and out when you breathe in deeply, and help push air out when you blow hard or cough. Together with the diaphragm they make the chest work like a bellows.
Set by your brainstem
You don't have to remember to breathe. A group of cells in the medulla, at the base of your brain, sets your breathing rhythm and speeds it up when carbon dioxide builds up in your blood, such as during exercise.