Other than The Anatomy Coloring Book (you have to be a certain age), I can't say I've paid much attention to my internal organs. Most of the time they all worked fine, so why worry? This lackadaisical attitude came to an abrupt end a few weeks ago when I suffered a collapsed lung — see illustration — marring 73 years, starting at age 5, of accident-free bicycling. Suddenly I had an investment in learning about lungs — their origin, how they work and how to recover full use of mine. Not to mention the arcane and painful business of chest tubes.
Lungs are a relatively recent innovation in the 4-billion-year saga of life on Earth. For 90 percent of its existence here, life got by fine without lungs because it only happened in the oceans. It wasn't until 400 million years ago, early in the warm Devonian Period, that plants established themselves on dry land (not counting non-vascular plants, like mosses, which emerged earlier). Some 20 million years later, plants were followed by tetrapod fish. Since tissues don't leave fossils, the exact time frame is speculative, but we do know that by 360 million years ago our audacious four-limbed ancestors had traded gills for lungs — possibly with swim bladders (sacs that allow fish to change buoyancy) as the intermediate step. The invention of lungs turned out to be a giant leap for animal-kind, since it's far more efficient to obtain oxygen from air than from water. The numbers tell the story: Air contains 21 percent free oxygen compared to less than 1 percent dissolved oxygen in water. (Fish can't extract oxygen directly from the strongly bonded H2O molecules of water.)
Fast forward to humans today. We breathe in and out about 12 times a minute, for roughly half a billion breaths in a lifetime. Unbidden, unappreciated. That's a lot of available oxygen for our 40 trillion cells to use for energy while excreting carbon dioxide as a waste by-product. Which, of course, is where lungs come in: They're essentially gas exchangers, swapping fresh-air oxygen for carbon dioxide.
Air enters the body via the nose and mouth, through the windpipe, thence to fork left and right into the lungs. The large tubes branch out into smaller and smaller airways that terminate in some 300 million alveoli — miniscule balloon-like air sacs arranged in clusters. Tiny blood vessels surrounding the thin-walled alveoli take up oxygen while simultaneously ridding the body of carbon dioxide. That may sound more efficient than it actually is; the exhaled air still contains about 15 percent oxygen (remember it went in as 21 percent) but obviously it's good enough to do the job of keeping us alive.
One happy adaptation that evolution came up with is that our two lungs are subdivided into five lobes, three on the right and two on the left, where the heart takes up space. Happily for me, anyway: Only my right superior lobe was punctured (a result of three fractured ribs), leaving the other four lobes to carry on regardless. Meanwhile, I can report that the insertion of a chest tube — to relieve pressure and drain fluid from the chest cavity normally occupied by the lobe — was worth the excruciating pain. It did the job in five days. Big appreciative sigh!
Barry Evans (firstname.lastname@example.org) can't say enough about the wonderful care he received during his five-day stay at St. Joseph Hospital.