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 body’s 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
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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
diseasedand 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
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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
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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
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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 man’s liability to many potentially fatal
or disabling lung disorders, including cancer, emphysema and bronchitis.
Typically, after years of smoking, pink, healthy lungs turn black.
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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.