What Happens To The Food In The Body
( Originally Published 1920 )
Preparing Food for the Body. You eat a great many different kinds of foods during the day—liquid foods such as milk, soft foods such as cereals, and perhaps some quite hard foods like nuts or hard crackers. You know that in some way these foods supply the energy for your daily life and that they are even built up into the organs of your body. You are growing, year by year and month by month, and every part of your body is getting bigger. The food you eat supplies the material for this growth; but it is not at all an easy thing to change oatmeal and poached eggs and milk toast into the muscles and nerves of a boy or girl.
The food, after being swallowed, passes into a tube called the alimentary canal, and before it gets really into the blood where it can be used, it must pass through the walls of the alimentary canal. In order to do this, the food must all be changed to a liquid form.
This process of changing the food so that the body can use it is called digestion. It is brought about by the action of the digestive juices, which are liquids prepared in the walls of the alimentary canal and in special organs connected with it. These liquids have the power of changing the foods in such a way that they can be passed. through the walls of the alimentary canal and taken into the blood.
The action of the digestive juices may be shown by a simple experiment. Take two glass test tubes, and in each put a piece of meat and a little water. To the second test tube add some of the digestive juice extracted from the stomach of a calf.' After the tubes have stood for half an hour in a warm place, the meat in the first tube will look just as it did at the beginning, but the tube containing the digestive juice will look cloudy and soft and the liquid will be discolored. This shows that the meat is being dissolved, or changed into liquid form, by the digestive juice.
You can easily observe the action of one of the digestive juices in your own body. Chew a piece of bread very slowly and thoroughly and see if you can notice a change in taste. While you chew, a digestive juice in the mouth becomes mixed with the bread. The starch in the bread is changed to sugar by the juice. Do you not notice that the bread tastes sweeter as this change takes place?
Parts of the Alimentary Canal.—The different parts of the alimentary canal are so important that you ought to learn the names of the principal ones, even though some of these names are long and hard to remember.
The general arrangement of the parts of the alimentary canal is shown in Fig. 39. The food, after it is swallowed, passes first down a long slender tube called the esophagus into a large bag or sac called the stomach. From the stomach, the food passes gradually out into a long coiled tube, the small intestine, and from there into a larger tube, the large intestine.
Digestion in the Mouth.—Two important steps in the process of digestion are taken in the mouth before the food is swallowed. First of all, it is broken up and softened by the action of the teeth. Secondly, it is mixed with the digestive juice of the mouth, which begins the digestion of the food by changing the starch in it to sugar.
It is very important to chew the food thoroughly before it is swallowed, if the rest of the digestive system is to be kept in good working order. The stomach is meant to digest soft, well chewed pulp, and if solid food is forced down in lumps, there is likely to be trouble. You remember, from Æsop's fable that was discussed in the second chapter of this book, how the stomach depends on the other organs of the body to help it in its work. One of the principal things it depends upon is the vigorous and thorough action of the teeth upon the food that is to be sent down to it for digestion.
Another reason, though a less important one, for thorough chewing of the food is the fact that the food tastes much better and we enjoy it more if it is eaten in this way. If you hive been in the habit of bolting your food, at your next meal try eating it quite slowly and chewing it thoroughly. See if you do not get more pleasure out of it.
Digestion in the Stomach.—The stomach is so large in comparison with other parts of the alimentary canal that it serves as a sort of storehouse for food. We need such a storehouse because the food, eaten in large amounts at mealtimes, must be digested slowly. It passes gradually from the stomach to the intestines. But though the storehouse is large, it cannot store the food of an over-hearty meal without making trouble.
In the walls of the stomach, there are strong muscles. These muscles, by contracting, keep the food moving round and round so as to break it up into a thin paste. At the same time more digestive juices are added to the food (particularly the kind of juices that dissolve meat, as shown in the experiment described on page 92).
After the food has been churned up in this way, and the digestive juices have acted upon it for a time, it is squeezed out from the stomach into the small intestine. The last of the food taken at an ordinary meal passes out of the stomach and into the intestine about four hours after it is eaten.
Digestion in the Intestines. We have seen how necessary the stomach is as an organ of digestion. The small intestine plays an even more important part in the process. This portion of the alimentary canal is slender, but it is very long. The food takes ten or twenty hours to pass through it.
In the course of its passage through the small intestine, the food mass is mixed with more digestive juices. Some of these juices come from the walls of the intestine itself. Some come from two organs, the liver and the pancreas, which pour them into the intestine. By the time the food has passed through the small intestine, most of the digestible matter in it has been changed into a liquid form.
Meanwhile the digested foods are being absorbed, or taken in, through the walls of the alimentary canal into the blood in the blood vessels. On one side of the thin, wall of the alimentary canal is the food, now digested and made liquid. On the other side of this wall is the blood. The food passes through the wall into the blood by a process called absorption. As the small intestine is very long, there is ample time for all the digested food to be absorbed there.
In the large intestine there is little more that needs to be done, except to store the undigested waste material until it is discharged.
The Wastes of the Body.—There are two kinds of wastes that must be regularly gotten rid of by the body. One kind is the undigested material from the alimentary canal. The other wastes are formed in the organs them selves in the course of their daily activity. Some of the wastes of this second kind are discharged into the air which we breathe out. Some are discharged in the perspiration formed by the skin. Some are discharged into the alimentary canal by the liver, a large organ which lies just above the stomach and empties into the small intestine; and the rest are gotten rid of by way of the kidneys.
The kidneys are two bean-shaped organs which take out water and certain waste materials from the blood and discharge them into a pouch called the bladder. The fluid formed by the kidneys is called the urine. The bladder should be emptied about six times a day.
Keeping the Digestion in Good Working Order.—If the digestive machinery is to be kept in good working order, it is of course necessary that it should not be supplied with too much food or with the wrong kind of food. It is also important not to exercise violently just after eating, for that prevents the digestive machinery from working properly. A cheerful, pleasant frame of mind helps to make digestion easy. Mealtimes should be times for pleasant talk and leisurely enjoy-ment, not for the hurried snatching of a bolted meal.
Another thing that is very important for the health of the digestive system and the body as a whole is the emptying of the large intestine by regular movements of the bowels. If the undigested food remains too long in the large Intestine, it decays, and poisons- are formed. These poisons may be absorbed into the body. A great many people have headaches and feel tired and half sick from this cause. A movement of the bowel% at least once a day and at a regular time is one of the most useful health habits that can be formed.