Lungs are Very Spongy and Elastic

Normally, the lungs are very spongy and elastic. When a breath is taken, the chest wall expands, expanding the sponge. Similar to the way a squeezed sponge will draw water into it when released, suction draws air into the lungs when the chest wall expands.

Air is brought though the trachea (windpipe) and bronchi (the main air tubes going to right and left lungs). These tubes divide into smaller and smaller tubes, finally ending in alveoli. Alveoli, the tiniest structures in the lung, are very small air sacs that are arranged like a bunch of grapes.

The alveoli are at the ends of the smallest tubes called bronchioles. The alveoli and the bronchioles are very important structures for the lungs to function properly. It is these structures that are destroyed by emphysema.

A sponge works to pick up water because all of the tiny little holes expand all at once after being squeezed. If the holes were larger, the sponge would not pick up as much water. This is because a larger hole cannot expand enough by itself to equal the action of multiple smaller ones.

Thinking of the lungs as a sponge in this way, it becomes easier to see how emphysema acts to cause impaired lung function. Lungs require an elastic quality, so that they can expand and contract well.

Additionally similar to the holes of the sponge, lungs need many alveoli (hundreds of millions, in fact) to draw enough air into them. The fewer and the bigger the alveoli, the less effectively they perform.