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Just as a fire needs oxygen to burn, the human body also needs a continuous supply of this essential element for the process of combustion that goes on constantly in every cell. We ordinarily do not think of a body metabolism as combustion, yet that is what is: the controlled burning of carbohydrates, fats, and proteins to provide energy. The job of the respiratory system is to furnish the oxygen that combines with these fuels in each of the billions of cells, and to carry away the waste product of carbon dioxide. And so we breathe fourteen times a minute, a pint of air per breath, more than ten thousand quarts of air a day. Not all that comes in, of course, is oxygen. Only about one fifth of the air we breathe is this life sustaining element.
But it makes up an important part of our bodies and our lives. At any given moment, half the bodys weight is oxygen. The overwhelming portion, incidentally, is not in the form of a gas, the way we usually think of oxygen. We loosely use the word respiration to describe the process of taking in oxygen and letting out carbon dioxide. To be scrupulously accurate, respiration refers to the ultimate exchange that takes place in the cells themselves, the delivery of oxygen and the removal of carbon dioxide. This gas transfer, as it is scientifically known, is at the heart of human life.
If oxygen did not arrive, if the carbon dioxide were not removed, our lives would be abruptly shortened. The exchange must take place in every cell, including those distant from the oxygen rich atmosphere that surrounds us. Obtaining that oxygen and starting it on its all important trip through the body begins with those critical organs, the page 2 lungs. A Look At The Lungs Although central to the vital and complex processes of all body cells, the lungs are mechanically simple in form, function, and principle.
They are cone shaped, pink in color, and weigh a little more than a pound each. The normal lungs of a healthy male have a capacity of nearly ten quarts. (Those of females are slightly smaller. ) Lungs are hardy organs. If one is diseased and removed, the respiratory process continues adequately without it. Of the two lungs, the right is larger as the heart takes more room on the left side.
Each lung is divided into lobes, which are fed by divisions of the bronchus, leading from the trachea (windpipe). The right lung has three lobes, upper, middle, and lower. The left has only two, upper and lower. The lobes are separate from one another and are marked by grooves on the surface, known as fissures. These give important information to doctors, as they can be seen on a chest x ray.
By looking carefully at their position and observing, for instance, whether they have moved up or down, they can tell whether you have suffered collapse of part of your lung. Locating The Lungs The lungs lie within the flexible rib cage. They normally have only one fixed attachment (at the larynx) and thus have considerable range of motion. The bases of the lungs rest above the diaphragm, the principal muscle breathing. Each lung is surrounded by a glistening membrane, the visceral pleura. The page 3 inner surface of the chest has a similar membrane, the parietal pleura.
Lubricate by fluids, these membranes glide smoothly against each other when we breathe. Normally there is no space between them, but entry of bacteria, penetrating wounds, or disease may separate the pleura. Inside The Lung The interior wall of the lung has a surface like a sponge. It is composed of more than three hundred million tiny alveoli, each scarcely more than a pinhead in diameter, and each open to the atmosphere at one end. The combined surface area of these sacs is so great that if they were flattened out, they would cover a tennis court. The alveolar walls are only a single cell thick, immediately beneath them, also encased in a wall of single cell thickness, is the capillary bed of the lungs.
How The Lungs Work If the lungs were removed from the chest, they would shrink like deflated balloons. They are held open by surface tensions, which is created by fluid produced by a thin lining around the lungs and the chest wall, the pleural membrane. To picture this, think of two sheets of glass. If dry and laid on top of one another, they can be easily separated, but if wet the surface tension of the water sticks the glass sheets together. The only way in which they can be separated is by sliding them apart. In the same way, as long as a thin layer of fluid separates the lungs from the chest wall, the lungs are held open.
When the chest expands the lungs are pulled out and air is taken into the alveoli millions page 4 of a tiny air sacs in the lungs, each surrounded by fine capillaries (blood vessels) where the exchange of oxygen and carbon dioxide takes place. When we exhale the rib muscles relax gradually. If we were to relax completely, the lungs would spring back rapidly. If air gets into the space between the lungs and the chest wall, the surface tension is broke and the lung collapses. If the lining membrane becomes inflamed or irritated it may produce an excess of fluid which accumulates in the space between the lungs and the chest. Commonly called fluid on the lungs, its medical description is a pleural effusion.
In the alveoli, the exchange of oxygen and carbon dioxide takes place in less than one tenth of a second. Oxygen is taken up by hemoglobin in the blood and the red cells discharge their load of carbon dioxide back into the alveoli, to be exhaled by the lungs. Lung Structure And Disorders In a normal lung, oxygen from the air is transferred to the capillaries that surround each alveolus. Some lung disorders include pneumonia, emphysema, asthma, bronchitis, and lung cancer. Pneumonia is where the air sacs are filled with fluid; emphysema is where the walls of the air sacs break down; asthma is when muscular walls of the bronchioles are narrowed; bronchitis is where the bronchus fills with mucus. In adults, bronchitis and emphysema are by far the commonest chest conditions in Western countries.
Over the last decade great progress has been made in prevention and page 5 treatment of several important cancers. Lung cancer is a disappointing exception. The lung cancer death rate for men has increased more than twenty five times since 1935. The number of lung cancer cases has more than doubled for both men and women. Five year survival rates are not improving significantly. Perhaps the grimmest aspect is that most of these cancer cases would not have occurred if the victims had not been cigarette smokers.
Cigarette smoking is unequivocally identified as the main factor behind the rise of lung cancer. Only ten percent of all lung cancer patients are nonsmokers. Certain industrial substances such as asbestos, nickel, chromium, arsenic, radon, and halogenated ethers also cause lung cancer, but smoking is clearly the most important risk factor. It is impossible to overstate the detrimental effects of smoking on health. A large number of factors combine to shorten the lives of cigarette smokers. Smokers have an increased risk of heart attack, and those smokers who do suffer heart attacks are less likely to survive than nonsmokers.
Smokers also run an increased risk of stroke. The tendency of cigarettes to induce chronic obstructive lung disease has already been mentioned, as has the greatly increased incidence of lung cancer in smokers. And pregnant women who smoke are more likely to have premature or stillborn infants. Smoking is known to increase mans liability to many potentially fatal or disabling lung disorders, including cancer, emphysema and bronchitis.
Typically, after years of smoking, pink, healthy lungs turn black. page 6 Our lungs are essential to life, yet they are frequently misused subjected to smoking or industrial pollution. Stopping smoking, although not a cure for lung disease, is definitely a preventive measure.
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