Every now and then you see pictures in the newspapers of men who are a foot or two taller than men of ordinary size. Also, you see pictures of men who are only two or three feet tall even though they are full- grown. Scientists have spent much time trying to find out why some people are very tall and some very short. Likewise, they have spent much time trying to find out why some people are thin and others fat.
How the Body Grows
The building materials of the body.
The body of every living thing is made up of tissues. Tissues, in turn, are made up of tiny cells. You might say that cells are the building blocks from which the tissues are made and that the tissues are the larger materials from which the body as a whole is made.
The simplest known form of life is a one-celled creature called the amoeba. This tiny creature looks more like a mass of jelly than anything alive, but it can take in and digest food and can move from place to place. There is no question, then, that it is alive. However, it has a very simple body. Most animals, as well as most plants, have complex bodies made up of many cells of many different kinds. Thus in the human body there are bone cells, muscle cells, nerve cells, and a number of others. These cells look different and work in different ways. Each makes up a special kind of tissue and has a special work to do.
How cells grow.
When a baby is born, its body is made up of different kinds of cells, just as is that of an adult, or grown-up. In order to grow it does not need more kinds of cells but more of the same kinds it already has. In other words, as the scientist says, multiplication of the cells is necessary. This means that they must separate into two parts to form new ones. Then, too, as cells work, they wear out. When this happens new ones must be formed to take their places. The building of cells, therefore, must continue from the time a person is born until he dies. It is most important, of course, when he is still young and growing.
In order for cells to grow, three things are necessary. First, they must have food. They get their nourishment from the blood, which picks up digested food from the intestines. Second, they must be active. If they are inactive, they become too weak to do their work well. Third, they must help the body get rid of waste materials, which are formed as they work. All of these things are necessary not only for growth but also for good health.
Cells fed by the blood.
Much of the food taken into the body is digested as it reaches the small intestines. Here, it finds its way into the blood, which in turn carries it to all parts of the body. The cells then take it from the blood.
The blood is pumped by the heart, a muscular organ on the left side of the body. This organ contracts, or beats, about seventy-two times a minute. Every time it beats it causes the blood to surge on its way through tubes known as arteries, the largest of which is the aorta. The effects of the beats may be felt in certain parts of the body, such as the wrist or temple, where an artery lies near the surface. Counting the surges or beats is known as “taking the pulse.” The arteries branch out in the body somewhat like the limbs of a tree. At the ends of the branches are tiny tubes known as capillaries, which join the arteries to other tubes known as veins. The veins carry the blood back to the heart. The largest veins are the vena cava superior, which returns the blood from the upper parts of the body, and the vena cava inferior, which returns it from the lower parts.
Every time the heart beats, it also sends blood to the lungs. Here the blood is purified by the air taken in during breathing. The tube which carries the blood to the lungs is known as the pulmonary vein and that which carries it back is known as the pulmonary artery.
The blood itself is made up of a liquid part known as lymph and countless tiny disc-like substances named corpuscles. There are two kinds of corpuscles, red and white. The red corpuscles help to bring oxygen to the cells from the lungs. The white corpuscles help largely to get rid of disease germs. There are many more red corpuscles in the blood than white. In fact, there are so many red corpuscles that they, more than anything else, give the blood its bright red color. The food is carried by the liquid part of the blood, or the lymph. When the lymph reaches the cells, it surrounds them, leaving the food and taking up waste materials.
The movement of the blood through the heart, lungs, arteries, capillaries, and veins is known as the circulation of the blood. This action is very important, for it distributes the food and helps to remove body wastes.
How much should you grow?
Nobody knows exactly how much you will grow. There may be very good reasons why you should not expect to be as tall as some of your friends. There may also be very good reasons why you should not expect to weigh as much. On the other hand, there may be very good reasons why you should become taller and weigh more. Your height and weight, though, are not especially important so long as you are healthy. Doctors, nurses, and others have made records of the weights and heights of thousands of children.
How Much the Body Grows
Effect of parents and grandparents.
Are your eyes of the same color as those of your father or mother? Is your hair of the same color? If so, you may be said to have inherited the color from your parents. Indeed, you may even have inherited it from your grandparents. The effect of parents and grandparents on a person’s body is known as heredity. Besides color of eyes and hair, people often inherit many other things, even size and shape. If your parents or grandparents were tall, for instance, you probably will also be tall. If, on the other hand, they were short, you, too, probably will be rather short.
In your later school work you will learn much more about heredity. You will also learn about a man named Mendel, who was one of the first to explain just how it works. He carried on many experiments with plants and finally explained heredity in a statement that is known as Mendel’s law. The leading thing that you need to remember at this time is that heredity may affect your growth. You may resemble your parents in some ways, your grandparents in others, and so on. In short, heredity helps to explain the manner in which you grow.
How glands affect growth.
Within recent years doctors and other scientists have learned that various glands affect the growth of the body. These glands are organs of various sizes which make special fluids known as secretions. There are two kinds of glands in the body. Some of them, such as the kidneys and sweat glands, are provided with outlets, or ducts, through which they pour’ their secretions. Others, known as ductless glands, have no ducts but pass their secretions directly into the blood. These are the ones that seem to have the greatest effect on growth. There are several ductless glands, but the two that affect growth the most are the pituitary and the thyroid, both of which have been very carefully studied during recent years.
The pituitary gland is located in the head below the brain. If this gland does not secrete as much fluid as it should, a child may never grow up. In other words, he’ may become a dwarf. If the gland secretes too much fluid, the body may grow much larger than it should. The thyroid gland is also located just below the brain but is somewhat farther down, where the neck and body meet. If this gland does not secrete enough fluid, it tends to make people dull and slow. If it secretes too much fluid, it tends to make people thin, nervous, and overactive. Doctors sometimes control growth by giving medicine to regulate these glands. No medicine of this kind, however, should be taken except upon a doctor’s orders or advice.
Some parts grow faster than others.
Often some parts of the body seem to grow faster than others. The bones, for example, may grow much more rapidly than some of the other tissues. This causes a child suddenly to become tall. Sometimes it seems that he has grown up almost over night. When this happens, his muscles do not help properly in moving his longer arms and legs. He cannot control his body well and is said to be awkward and clumsy. Later, as his muscles grow, he becomes less awkward and finally moves about with grace and ease. Any boy or girl who feels such awkwardness should not be discouraged, however, for sooner or later it will pass away.
Why people stop growing.
People in general stop growing when they have reached the size best suited to their needs. Scientists say that they stop growing when they are best adapted to their environment. They stop growing .for the same reason that most animals are adapted to their environment. The elephant, for example, has a large body which makes it well adapted to the jungles of India. It can push its way through the trees and bushes and get plenty to eat from the dense tropical forests. The polar bear, on the other hand, is adapted to the cold lands of the North and would probably starve to death in the jungle.
There are many kinds of plants and animals, but most of them are adapted to certain environments. If they are taken from these environments, they either die or do not live so well. Man is the most adaptable of all living creatures. He can live in almost any climate and in almost any part of the earth. He probably would not be able to do so if he were as large as an elephant or as small as a mouse. Thus nature has decided about how large a man should be to fit his needs in life.
Helping the Body to Grow
Importance of sunshine and pure air.
If a few potatoes are left on the cellar floor until late in the spring, something strange will happen. They will shoot forth sprouts just as if they were planted in the ground. These sprouts, however, instead of looking strong and healthy, will be sickly white in color. Moreover, no leaves will grow and, of course, no new potatoes will form. In other words, nature will try to produce a crop of potatoes but will make a complete failure of it.
Sunshine and fresh air are just as much needed for the growth of the body as for the growth of potatoes. Children who live in dark basements or crowded tenement houses often never gain their full size. Their faces look pale and thin. Their muscles are weak and flabby. Usually they do not run and play as do children who live in more open places. Children who work in mines and factories of ten look and act the same way. They may not have heavy loads to carry nor extra long hours for work, but the lack of sunshine and pure air keeps them from growing and being in healthy condition. This explains why many states have laws forbidding children to work in mines or factories or regulating the conditions under which they may work.
Need for exercise and rest.
Exercise is necessary to help remove the waste materials from the cells. As these cells work, they always burn up food materials and give off waste materials. The more active the cells are, the more healthy they are, and the better a person feels. Thus exercise gives the body what is known as a good muscle tone. This means that a person is filled with a desire to be doing things. Children, especially, should have this feeling, and should always be eager for work or play.
When the body is at work, the cells are not repaired as rapidly as they are worn out. The waste materials are not removed as rapidly as they are formed. Rest and sleep are necessary to give the body an opportunity to build up the cells and to carry off the surplus waste materials. “Time out” is needed for rest, whether a person is working or playing. It is for this reason that school programs are planned to provide for play as well as for work during the day. It is for this reason, also, that you go to bed at night and secure as much rest as you can.
Need for cleanliness.
Growth, as you know, depends on the repair of worn-out cells and the increase in the number of cells. Cell growth and repair can take place only when the body is in a healthy condition. The waste must always be removed so that the cells do not become clogged with worn-out materials. Cleanliness is necessary to help the body get rid of the worn-out materials. If people live in homes that are carelessly kept or work in dirty places, the pores in their skins become closed, and perspiration cannot carry away the waste as rapidly as necessary. Even people who live in clean homes and work in clean places should bathe often to keep the pores open.
People have not always understood the importance of bathing. There was a time when children were sewed into their clothes in the fall and did not take them off until spring. People once thought that bathing every day or so was very dangerous. About a hundred years ago, for example, some of the states passed laws forbidding people to build bathtubs in their homes. These facts are hard to believe, but they show how knowing more about the body has led people to take better care of themselves. Today babies must have baths, children must have baths, and, in fact, everybody must have them frequently if he is to feel well and be healthy.
The effect of foods.
No one knows better than the farmer how much good there is in foods. Much of his time is spent in raising and storing feed for animals on the farm. He studies carefully what his horses, cows, hogs, and chickens will need. He is careful to give them not only the right kind of feed but the right quantity as well. This is because (1) he takes pride in them, and (2) he wants them to grow in such a manner as to yield a good profit when sold.
Foods are just as important for a child as feed is for growing animals on the farm. Were it not for foods the cells would not grow or do their work. These foods must be of various kinds. A great deal of one kind is not sufficient. Farm animals need only a few kinds of feed, but a human being needs a much greater variety of foods. Not only must a child have the right kinds of food, but he must eat them. under pleasant conditions. Mealtime must be a happy time, and he should look upon eating with very great pleasure.