How Lungs Work

Imagine our lungs as a very thin sheet of tissue about the size of a tennis court (about 400 square feet) surrounded by air and connected to your bloodstream.

Now imagine your heart pumping blood to, from and through this rather large sheet of tissue. One side of your heart receives blood carrying carbon dioxide from the cells of your body and the other side of your heart receives blood loaded with oxygen collected by passing it through this large tissue sheet. The blood loaded with carbon dioxide is sent by your heart through this sheet of tissue where the carbon dioxide is released from your blood through the very thin tissue walls by a process called diffusion. The same process that causes perfume to spread from where there is a high concentration of perfume (like when you drop and break a bottle) to the rest of the room where there wasn't any to start with. Gases like carbon dioxide and oxygen work the same way.

OK, now we’ve gotten rid of the carbon dioxide, but now we need to get that oxygen our body needs.
Blood cells contain a molecule called hemoglobin. This molecule is what gives our blood its red color. Hemoglobin loves to grab onto the oxygen molecules diffusing (remember the perfume?) through this thin, flat really big piece of tissue from the surrounding air. The ‘oxygenated’ blood is returned to your heart and pumped throughout your body to your cells. The hemoglobin releases the oxygen to the cells which 'burn’ it, to provide the energy for all the things our bodies have to do, and in the process convert it to carbon dioxide which our amazing plumbing system returns to our large sheet of tissue to begin the process all over again.

Now it would be a little difficult to try and drag this tennis court sized tissue around all day, so the body does something very clever. It achieves the high surface area it needs, to do all this diffusion, by dividing it into about three hundred million tiny, hollow sacs called alveoli (little balloon-like sacs the size of grains of salt) which line the walls of two larger sacs called lungs. Although the surface area of each of these tiny sacs is small, with millions of them you can get the same surface area as our flat sheet of tissue. The tiny sacs are lined with really tiny blood vessels called capillaries that allow the exchange of the carbon dioxide and oxygen.

Air enters our lungs by way of what we commonly refer to as our windpipe which branches into ever tinier and tinier tubes eventually branching into tubes tiny enough to lead into the tiny air sacs, the alveoli. When you exhale the alveoli deflate expelling carbon dioxide laden air in to the lungs and when you inhale they inflate taking in oxygen rich air. This is what we call breathing.

But you probably already guessed that.