”I am Your Body”

LUNG

    
I AM YOUR right lung, and I claim the privilege of speaking since I am slightly larger than my partner in the left side of your chest. I have three lobes - sections - while the left has only two. You would be surprised if he could see me. You think of me as a kind of hollow, pink football bladder hanging in your chest. I'm not much like that at all. I am not hollow - if you cut through me, I would look something like a rubber bath sponge. And I am not pink. I was when you were a baby. Now, a quarter of a million cigarettes (I hope your a none smoker) plus half a billion breath of dirty city air later, I am an unattractive slate-gray with mottling of black.
There are three separate, sealed compartments in your chest: one for me, one for the left lung, and one for your heart. I hang loose in my compartment, filling it completely, and weigh a little over a pound.

I have no muscles and hence play a passive role in breathing. There is a slight vacuum in my compartment - so when your chest expands, I expand. When you exhale, I collapse. It is simply a recoil mechanism. Puncture your chest wall in an accident and my vacuum is broken. I'll hang loose; doing no work, until healing takes place and the vacuum is re-established.

Take a closer look at my architecture. Your four-inch-long windpipe divides at its lower end into two main bronchial tubes - one for me, one for my partner. Then branching begins in me - like an upside down tree. First the larger bronchi, then the bronchioles 1/100 of an inch in diameter. These are simply air passages. My real work is done in my alveoli - grapelike bunches of minute air sacs. Flattened out, their tissue would probably cover half a tennis court.

Each alveolus is covered with a cobweb of capillaries. Blood is pumped by the heart into one end of a capillary. Red cells pass through single-file - the passage taking about a second - and a remarkable thing takes place. Through the gossamer membrane of the capillary wall, the cells diffuse their cargo of carbon dioxide into my alveoli. At the same time, the cells pick up oxygen going the other way. It's a kind of gaseous swap shop - blue blood flowing in one end of the capillary, emerging refreshed and cherry-red at the other.

Your more important body organs - notably the heart - are under automatic control. Most of the time this is true of me, too, though I am under voluntary control as well. As a child, you had temper tantrums and would sometimes hold your breath until you turned a faint blue. Your mother worried, unnecessarily. Long before you got into any trouble, automatic respiration would take over. You would start breathing whether you wanted to or not.

My automatic breathing control is in the medulla oblongata - the bulge where the spinal cord taps into the brain. It's amazingly sensitive chemical detector. Laboring muscles burn oxygen rapidly and pour out waste carbon dioxide. As it accumulates, the blood becomes slightly acid. The respiratory control center detects this instantly and orders me to work faster. Let the levels rise high enough, as when your doing heavy exercise, and it orders deeper breathing as well - one's "second wind".

Lying quietly in bed, you need about eight quarts of air a minute. Sitting up requires l6; walking, 24; running, 50. If you are a desk-worker, you have no large oxygen demand. Normally, you breathe about 16 times a minute - a pint of air each time. (This only partially inflates me. I can hold eight times as much.) Even so, not all of that one-pint breath reaches me; one third of it shuffles aimlessly in and out of the windpipe and other air passages.

I like my air just about as moist and warm as that in a tropical swamp. Producing this very special air in the space of a few inches is quite a trick. The same tear glands that bathe your eyes, plus other moisture secreting glands in your nose and throat, produce as much as a pint of fluid a day to humidify my air. Surface blood vessels along the same route - wide open on cold days, closed on warm days - take care of the heating job.

There is an almost endless list of things that can cause me trouble. Each day, you breathe in a variety of bacteria and viruses. Lysozyme in the nose and throat, a powerful microbe slayer, destroys most of these. And those that slip into my dark, warm, moist passages - a microbial happy hunting ground - I can usually handle Phagocytes patrol my passages and simply wrap themselves around invaders and eat them.

Dirty air, of course, is my biggest challenge. Other organs lead sheltered, protected lives, but for all practical purposes I am outside your body - exposed to environmental hazards and contaminants. I am really quite delicate, and it's a wonder I am able to survive at all, having to deal with such things as sulfur dioxide, benzopyrene, lead, and nitrogen dioxide. Since some of them actually melt nylon stockings, you can guess what they do to me.

My air cleaning process - such as it is - begins with hairs in the nose, which trap large dust particles. Sticky mucus in nose, throat and bronchial passages acts as flypaper to trap finer particles. But the real cleaning job falls to the cilia. These are microscopic hairs - tens of millions of them - along my air passages. They wave back and forth, like wheat in the wind, about 12 times a second. Their upward thrust sweeps mucus from lower passages to the throat, where it can be swallowed.

If you could watch my cilia under a microscope, you'd see that if cigarette smoke or badly contaminated air is blown on them, action stops. A temporary paralysis sets in. Let this irritation continue long enough, and the cilia wither and die, never to be replaced.

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