The Respiratory System
( Originally Published 1917 )
Our Need of Oxygen.—We hardly ever think of the atmosphere about us, except when the wind sets it in motion. Yet the air is a very real substance, as you can feel when you press on a paper bag which has been blown up full of it. This "atmospheric ocean forty-five miles in depth, surrounding our planet, and whirling with it as it whirls around the sun," is made up of two gases, nitrogen and oxygen—about one-fifth oxygen and four-fifths nitrogen, with small traces of other gases.
All living things need oxygen to make life possible, and animals and human beings get their necessary oxygen from the air by the process of breathing. This is why respiration is a sign of life. If a person is seriously injured and unconscious, our first impulse is to see whether he is still breathing.
Oxygen and the body tissues act upon each other so that each is changed in certain ways; we say that the oxygen reacts with the body tissues. This process is called oxidation. Oxidation in the body has been compared, in Chap-ter I, to the process that goes on in the fire box of a furnace when the oxygen in the draft of air reacts with the fuel to produce heat energy. In somewhat the same way, although by a longer and more complicated process, breathing furnishes oxygen to react with the body material and to pro-duce life energy.
The Objects of Respiration.—Sometimes when the fire in a furnace or a stove burns badly, you can smell some of the gases formed by the reaction between the fuel and the oxygen. When the fire burns well, however, the chief thing given off is the gas carbon dioxide, which has no smell. The
same gas is formed by the oxidations within the body, and in order to keep the human machine at work, the lungs must obtain a new supply of oxygen and get rid of the carbon dioxide formed in the tissues. This double process is the object of respiration.
The effect of the exchange of gases in the lungs is indicated by the fact that while the air inhaled is 21 per cent oxygen and only .03 per cent carbon dioxide, the air exhaled is only 16 per cent oxygen and 4 per cent carbon dioxide. It is easy to show the presence of carbon dioxide in the breath by breathing through a glass tube into limewater; a peculiar milkiness will appear as a result of a reaction between the lime and the carbon dioxide.
The Air Passages acid the Lungs.—When you breathe properly, through the nose, the air goes through the nasal passages into the back of the throat, for the nose at the back opens into the throat. From the throat the air passes, by way of the larynx, into a tube called the trachea or wind-pipe (see Figs. 40 and 41), which opens out of the front of the throat just below the mouth. The opening. from the throat to the windpipe is closed by a little door, the epiglottis.
If a particle of food gets by this door and into the windpipe, violent coughing follows, in the effort to dislodge it.
The trachea branches at its lower end into two smaller tubes, the bronchi, each of which in turn opens into one of the lungs. The lungs are large sacs or pouches which lie one on each side of the chest. As the bronchi enter the lungs, they branch and subdivide again and again, and each branch finally ends in a tiny sac. There are about 725,000,000 of these little sacs in the lungs, and if their surfaces could all be spread out side by side they would cover 2150 square feet. When we take a deep breath, each of these sacs fills with air and swells up like a toy balloon.
In the walls of the small sacs are blood vessels, which are separated by a very thin wall from the air in the lungs. It is through this thin wall that oxygen passes from the air to the blood and, in exchange, carbon dioxide passes from the blood to the air.
The Mucous Membranes of the Nose and Throat—It has been pointed out in an earlier chapter that the walls of the digestive canal are lined with a peculiar soft moist tissue known as mucous membrane. The respiratory passages of the nose and throat are lined with the same kind of membrane.
The tissue cells of this mucous membrane in most parts
of the respiratory system are provided with tiny finger-like cilia or lashes, which move back and forth, but much more quickly and strongly in one direction (toward the mouth and nose) than in the other. By this motion they sweep along any dust or dirt which has been inhaled and has clung to the moist mucous sufaces, sending it toward the nose or throat, where we get rid of it.
Ordinarily this sweeping action of the cilia keeps the mucous membranes free from harmful microbes. When such microbes settle down and grow on the respiratory surfaces, disease may follow. Colds and catarrh result when the nose and upper part of the respiratory system are affected, bronchitis when the germs are in the bronchial tubes, and pneumonia if the infection reaches the lungs.
The Organs of Speech.—In the trachea, just below the point where it connects with the throat, is the larynx or voice box. Here many of the sounds of speech are made, by the vibration of two bands called the vocal cords, which work somewhat like the strings of a violin. When you talk, you can feel the larynx move if you place your fingers on your throat just under the chin, at the place where the air passes from the throat into the trachea. A man's voice is deeper than that of a child or a woman because his vocal cords are larger and longer and make a sound lower in pitch. At a certain period in the growth of a boy, his larynx suddenly grows very much larger and the vocal cords lengthen. We say his voice is "changing." Care should be taken not to strain the voice at this time, for it may be seriously harmed.
We do not speak with our vocal cords alone. Many of the sounds are made with the help of the lips, teeth, and tongue. A pleasant voice is one of the most attractive gifts a person can have, and lips, tongue, and larynx can in large measure be trained to produce clear and beautiful speech.
The Process of Breathing.—You have been breathing all your life, some 30,000 times every twenty-four hours, yet you have never had to think about it unless you have perhaps tried to "hold your breath" for a few seconds. It is interesting to know how the body brings about this wonderful rhythmic movement of the air.
Across the bottom of the chest space stretches a sheet of muscle, called the diaphragm, which divides the inside of the trunk into an upper and a lower part. It is the upper part or thoracic cavity which contains the lungs. The walls of this cavity are supported by the ribs, which slope down-ward and forward to the breastbone (see Fig. 43). At the back they are attached to the backbone. When the muscles between the ribs contract, the breastbone and the front ends of the ribs are raised; and since they are hoop-shaped, the thoracic cavity becomes larger from side to side and back to front, as they rise. At the same time, the domeshaped-diaphragm also contracts (pulls downward) and tends to enlarge the central part of the thoracic cavity. All these muscles contract together regularly about twenty times a minute, making the chest space larger at each contraction and smaller at each relaxation.
Each time the chest space grows larger, the elastic walls of the lungs stretch so that the lungs fill the enlarged space. More air must, of course, be drawn into the lungs to fill them. This act of breathing in is called inspiration.
At expiration (breathing out), the process is reversed. The chest space is made smaller because the ribs fall back into place, and the diaphragm rises. The chest space is thus compressed, and the elastic walls of the lungs are forced in, so as to drive out some of the air.
This machinery is so wonderfully controlled by the inner adjustment of the body that it supplies just the amount of air the body needs. You know that when you run, you breathe hard and fast. As your muscles work harder, they need more oxygen and form more carbon dioxide, and without any thought on your part your breathing apparatus adjusts itself accordingly.
How to Breathe Well.—Though the inner machinery of the body takes care that we breathe so as to get the amount of oxygen the body needs, it does not follow that the lungs will keep healthy without care on our part.
When a person slouches in walking, bends over a desk all day, or wears tight clothing that binds the ribs and the abdominal muscles, the chest cannot expand properly. Under such conditions, a person takes short breaths and does not get the air into the deeper parts of the lungs. The portions of the lungs near the bronchi do all the work, and the lower parts, lacking the necessary exercise, are likely to become diseased. This is one reason why clerks and telegraph operators, and other people who sit much of the time in a cramped position, frequently suffer from tuberculosis. In order to have sound, healthy lungs, it is important to form good breathing habits. In walking, standing, and sitting, the head should be held high and the chest out.
Every one pities a narrow-chested man or woman; but scarcely any boy or girl need grow up with a small chest, for it can easily be enlarged by proper position and exercise. You should breathe slowly and deeply; if this is not natural, practice for a little while every day till it becomes a habit. Always breathe through the nose and not through the mouth, because the nasal passages are made in such a way that they warm and moisten the air and strain out its impurities as it is inhaled. Mouth breathing is a bad habit and should be overcome. If it cannot be corrected by a little thought and effort, there may be something wrong which needs medical care.
Adenoids and Tonsils.—Sometimes mouth breathing and difficulty in breathing are due to growths in the throat, and it is important that this condition should be promptly remedied.
Adenoids are finger-like, spongy growths which develop in the back of the throat where the nose opens into it (see Fig. 44).
The tonsils are roundish organs on each side of the throat (see Fig. 44). They often grow to be too large, or become diseased in some way. Bad tonsils are likely to become infected with bacteria and to lead to tonsilitis and other more serious diseases.
Effects of Smoking.—The habit of smoking always results in injury to the air passages, and a cough and "smoker's sore throat" are often caused by the use of tobacco. Inhaling, or taking the smoke into the lungs, is a particularly dangerous habit, since in this way the poisons in the smoke pass directly into the blood and thence to all parts of the body. One of the reasons that cigarette smoking is so harmful is that the smoke of a cigarette, being milder than the smoke from a pipe or a cigar, is much more likely to be inhaled.
QUESTIONS FOR DISCUSSION AND REVIEW
1. What facts do you know about the air?
2. Hold your nose and keep your mouth tightly shut. How many seconds is it before you are uncomfortable? Why?
3. How long can you stay under water in a dive?
4. Why do we need oxygen?
5. We hear stories of lowering a lighted candle into a well or unused cellar before any one dares to go down. What is the object?
6. What waste product of bodily activity is thrown off by the lungs?
7. Name the organs of respiration through which the air passes to get into the lungs.
8. Explain how the air and the blood exchange oxygen and carbon dioxide in the lungs.
9. What becomes of the dust in the air we breathe?
10. What is a cold in the head? Bronchitis? Pneumonia? I r. How is the voice produced?
12. What causes a boy's voice to become deeper when it "changes"?
13. Say the different letters of the alphabet and see which do, and which do not, require the use of the teeth and tongue.
14. What muscle separates the thoracic and abdominal cavities? What part does this muscle play in the process of breathing?
15. How is the chest enlarged to allow the air to enter the lungs?
16. How is the air forced out of the lungs in respiration?
17. Watch the breathing of some of the people you know. Do you think they use all of their lung tissue?
18. What habits may interfere with deep breathing?
19. If you saw a child who kept his mouth open most of the time and gasped for breath after closing it for a few minutes, what would you conclude was the matter?
20. Take a hand glass and try to locate your tonsils. Are they pink or red? Which should they be?