WHAT an interesting story your lungs could tell—if only they could talk! Not only could they give you some startling facts about their size and delicate design, but they could also describe how they function, and the fight they sometimes have to put up to keep you alive. But since your lungs cannot talk, you will have to get their fascinating story from outside investigators.

You can survive without food for weeks. Some have fasted forty or fifty days. And you can get along without water for days, as has been the experience of shipwrecked sailors in the midst of the salty ocean. But you cannot get along for more than a few minutes without breathing. That is how important your lungs are to you.

Most people just take their lungs for granted, and, for ever so many people, they function noiselessly and efficiently most of the time, from the cradle to the grave. In fact, when your lungs do make themselves known you are already in trouble. So you had better give them some thought and good care before it is too late.

Your lungs are two conical or pyramidlike organs that weigh about one and a fourth pounds each in adults. In men they account for one thirty-seventh of the body weight, in women one forty-third. Your right lung consists of three sections or lobes; your left has only two lobes because of the room that the heart takes up in the chest. At birth your lungs are a pinkish white, but with the passing of the years they get to look a mottled and slatey gray, and in old age may even show black spots. Although your two lungs can hold from six to seven quarts of air, this does not mean that they are large hollow, bellowslike organs. Were you to cut them open, you would find that they somewhat resemble foam rubber sponge.

The air you breathe enters your nose and mouth and then flows through the pharynx, larynx and trachea or windpipe. The windpipe branches into two tubes known as the bronchi, which enter the rear of each lung at about the middle. The windpipe and the bronchi are surrounded by heavy rings of cartilage in order that no crushing by external objects can stop air from flowing into the lungs.

The two main branches or bronchi, upon reaching the lungs, divide into four branches, the four into eight, and so on for some twenty more times until there are a million or more of these tiny branches known as bronchioles. The smallest of these is but one hundredth of an inch in diameter. At the end of the bronchioles are air sacs with tiny cup-shaped protrusions known as alveoli. Throughout your lungs there are as many as 300 million of these; some estimates even being as high as 750 million. These tiny alveoli, if spread out, would cover an area of a hundred square yards or more.

Each one of these tiny alveoli is covered with a web of capillaries. Through the walls of these tiny capillaries the oxygen comes in contact with the blood so that the body’s cells, in turn, can be supplied with oxygen for the purpose of producing energy. The oxygen is transported to the cells throughout the body by the hemoglobin in the red corpuscles. If laid end to end, these capillaries would extend hundreds of miles. Incidentally, these capillaries are just big enough for one red corpuscle to go through at a time.

Of course, the flow back and forth of oxygen and carbon dioxide through the walls, from alveoli to corpuscles, is over a distance far less than the thinnest paper you ever saw, less than a thousandth of a millimeter!

In a year’s time your lungs inhale from two to five million quarts of air. When filled to capacity, they contain from six to seven quarts of air. Yet, when you exhale, usually two quarts of air remain, although you can exhale purposefully to the point of having but one quart of air remaining. When you are taking it easy, resting on a couch or contour chair, you may be inhaling as little as a pint of air at a time, from ten to fourteen times a minute, or five to seven quarts of air a minute. However, when doing heavy work or engaging in vigorous exercise, you may take in as much as 80 to 120 quarts of air a minute, not so much by breathing faster as by breathing more deeply.

To understand how your lungs serve in supplying you with air, you need to understand another fact about them. Each lung is encased in a ‘skin’ called a “pleura” that is airtight. That is why you can take a freshly removed lung from an animal and blow it up like a balloon or football by pumping air into its windpipe. Not only that, but each of your lungs is housed in an airtight cavity having its own skinlike pleura.

How You Breathe

There are two basic kinds of breathing by which your lungs are filled and emptied: voluntary and involuntary. Your heart and your stomach are limited to involuntary action, you cannot deliberately speed up or slow down their activity. On the other hand, your limbs, your lips and your tongue act more or less according to your will or the habits you form. But your lungs are capable of both voluntary and involuntary actions. In voluntary breathing you cause the rib cage to expand and the diaphragm to lower, thereby drawing more air into your lungs.

Involuntary breathing is controlled by a “respiration center” in the lower part of that section of the brain known as the medulla. It stimulates the diaphragm to contract, causing it to lower and at the same time causing the ribs to move upward and outward. The result is a relative vacuum, a state of lower air pressure in the lungs than on the outside. This causes the air from the outside to be drawn into the lungs. Other nerve centers regularly interrupt this contracting action, allowing the chest muscles to relax and thus forcing the air out of the lungs.

Interestingly, this “respiration center” is not activated by lack of oxygen in the lungs but by the amount of carbon dioxide in your blood. The more carbon dioxide in your blood the more danger you are in and so the “respiration center” steps up the breathing process to keep the carbon dioxide content from reaching the danger point. Usually there is only a fraction of 1 percent of carbon dioxide in the air when it is inhaled. About 21 percent of the air breathed in is oxygen, but when exhaled it still contains about 16 percent. So you see, your lungs remove only about one-fourth of the oxygen in the air. The carbon dioxide increases proportionately, so that the exhaled air contains more than 4 percent carbon dioxide.

Conditioning the Air

It is obvious that, for your lungs to do their part right, the air must also be just right. It must be clean, it must be moist and it must be at the right temperature. And for this the Creator of the human body has supplied it with what men choose to call the “upper respiratory system.” All the passages through which the air flows before it reaches your lungs aid in meeting these three essential conditions. The nose has comparatively long hairs that catch the larger particles of dirt, which may be laden with bacteria. Its passages are also lined with mucous membranes so shaped as to catch the small particles. Still smaller particles are caught by the cilia, mucus-covered hairlike ridges in the windpipe that sway like wheat in a field. This motion causes any particles gradually to move up toward the throat, where they can be swallowed or spit out. White blood cells take care of any tiny bacteria that manage to get through these defenses.