Little cubes in the air sacs
Deep in your lungs are hundreds of millions of tiny air sacs called alveoli. Most of each sac wall is made of super-thin, flat cells. That's where oxygen passes into your blood.
Type II pneumocytes are different. They are small, plump, and roughly cube-shaped. They sit here and there in the sac walls, and they're packed with little bundles of a special liquid.
Wow!
If you could spread out all the air sac walls in your lungs, they would cover a huge area, roughly the size of a tennis court!