Your Lungs Contain 1,500 Miles of Airways

If you stretched out your lungs, the airways would run 1,500 miles - from London to Athens.

Inside is a fractal tree. Your trachea splits into two bronchi, then smaller bronchi, bronchioles, then 300-500 million tiny sacs called alveoli. 23 generations deep.

Laid end to end, those tubes measure about 2,400 kilometres. Unfolded, the alveoli create 70 square metres - half a tennis court - packed into a chest the size of a shoebox. You breathe 10,000 litres of air per day but use only a fraction at rest.

Destroying even a small percentage removes miles of airway, which is why lung disease is so devastating. Evolution packed a forest inside you.