A Handbook of Health by Woods Hutchinson (learn to read books .txt) 📖
- Author: Woods Hutchinson
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"But," some of you will ask at once, "what is to prevent the blood in the heart, when the muscle wall squeezes down upon it, from shooting backward into the vena cava, instead of forward into the aorta?"
Showing the strands of muscle that compose it, the arteries and veins that feed and drain the muscle coat, and fat protecting these.
Nature thought of that long ago, and ingeniously but very simply guarded against it by causing two little folds of the lining of the blood pipes to stick up both where the vena cava enters the heart and where the aorta leaves it, so as to form little flaps which act as valves. These valves allow the blood to flow forward, but snap together and close the opening as soon as it tries to flow backward. While largest and best developed in the heart, these valves are found at intervals of an inch or two all through the veins in most parts of the body, allowing the blood to flow freely toward the heart, but preventing it from flowing back.
As the heart has to pump all the blood in the body twice,—once around and through the lungs, and once around and through the whole of the body,—it has become divided into two halves, a right half, which pumps the blood through the lungs and is slightly the smaller and the thinner walled of the two; and a left half, which pumps the purified blood, after it has come back from the lungs, all over the rest of the body.
Each half, or side, of the heart has again divided itself into a receiving cavity, or pouch, known as the auricle; and a pumping or delivering pouch, known as the ventricle. And another set of valves has grown up between the auricle and the ventricle on each side of the heart. These valves have become very strong and tough, and are tied back in a curious and ingenious manner by tough little guy ropes of tendon, or fibrous tissues, such as you can see quite plainly in the heart of an ox. It is important for you to remember this much about them, because, as we shall see in the next chapter, these valves are one of the parts of the heart most likely to wear out, or become diseased.
In A the blood flows forward naturally. In B and C is shown what would happen were the blood to reverse its course, as it does when it meets an obstruction: the pockets would fill until they met and closed the passageway.
Heart Beat and Pulse. The heart fills and empties itself about eighty times a minute, varying from one hundred and twenty times for a baby, and ninety for a child of seven, to eighty for a woman, and seventy-two for a full-grown man.
When the walls of the ventricles squeeze down to drive out their blood into the lungs and around the body, like all other muscles they harden as they contract and thump the pointed lower end, or apex, of the heart against the wall of the chest, thus making what is known as the beat of the heart, which you can readily feel by laying your hand upon the left side of your chest, especially after you have been running or going quickly upstairs. As each time the heart beats, it throws out half a teacupful of blood into the aorta, this jet sends a wave of swelling down the arteries all over the body, which can be felt clearly as far away as the small arteries of the wrist and the ankle. This wave of swelling, which, of course, occurs as often as the heart beats, is called the pulse; and we "take" it, or count and feel its force and fullness, to estimate how fast the heart is beating and how well it is doing its work. We generally use an artery in the wrist (radial) for this purpose because it is one of the largest arteries in the body which run close to the surface and can be easily reached.
Summary of the Circulation of the Blood. We will now sum up, and put together in their order, the different things we have learned about the circulation of the blood through the body.
R.A., right auricle; L.A., left auricle; R.V., right ventricle; L.V., left ventricle; A, aorta; P.A., pulmonary artery; P.V., pulmonary veins; V.C.s., Vena cava superior; V.C.i., Vena cava inferior. At the entrance to the pulmonary artery are shown two of the pockets of the valve, the third pocket having been cut away with the front side of the artery. The other blood-tubes have similar valves, not shown in the diagram.
Starting from the great vein trunk, the vena cava, it pours into the receiving chamber, or auricle, of the right side of the heart, passes between the valves of the opening into the lower chamber, the right ventricle. When this is full, the muscles in the wall of the ventricle contract, the valve flaps fly up, and the blood is squirted out through the pulmonary artery to the lungs. Here it passes through the capillaries round the air cells, loses its carbon dioxid, takes in oxygen, and is gathered up and returned through great return pipes to the receiving chamber, or auricle, of the left side of the heart. Here it collects while the ventricle below is emptying itself, then pours down between the valve flaps through the opening to the left ventricle. When this is full, it contracts; the valves fly up and close the orifice; and the blood is squirted out through another valve-guarded opening, into the great main artery, the aorta. This carries it, through its different branches, all over the body, where the tissues suck out their food and oxygen through the walls of the capillaries, and return it through the small veins into the large vein pipes, which again deliver it into the vena cava, and so to the right side of the heart from which we started to trace it.
Although the two sides of the heart are doing different work, they contract and empty themselves, and relax and fill themselves, at the same time, so that we feel only one beat of the whole heart.
One of the most wonderful things about the entire system of blood tubes is the way in which each particular part and organ of the body is supplied with exactly the amount of blood it needs. If the whole body is put to work, so that a quicker circulation of blood, with its millions of little baskets of oxygen, is needed to enable the tissues to breathe faster, the heart meets the situation by beating faster and harder. This, as you all know, you can readily cause by running, or jumping, or wrestling.
CHAPTER XII THE CARE OF THE HEART-PUMP AND ITS PIPE-LINESThe Effect of Work upon the Heart. Whatever else in this body of ours may be able to take a rest at times, the heart never can. When it stops, we stop! Naturally, with such a constant strain upon it, we should expect it to have a tendency to give way, or break down, at certain points. The real wonder is that it breaks down so seldom. It has great powers of endurance and a wonderful trick of patching up break-downs and adjusting itself to strains.
Every kind of work, of course, done in the body throws more work upon the heart. When we run, or saw wood, our muscles contract, and need more food-fuel to burn, and pour more waste-stuff into the blood to be thrown off through the lungs; so the heart has to beat harder and faster to supply these calls. When our stomach digests food, it needs a larger supply of blood in its walls, and the heart has to pump harder to deliver this. Even when we think hard or worry over something, our brain cells need more blood, and the ever-willing heart again pumps it up to them. This is the chief reason why we cannot do more than one of these things at a time to advantage. If we try to think hard, run foot races, and digest our dinner all at one and the same time, neither head, stomach, nor muscles can get the proper amount of blood that it requires; we cannot do any one of the three properly, and are likely to develop a headache, or an attack of indigestion, or a "stitch in the side," and sometimes all three. So the circulation has a great deal to do with the intelligent planning and arranging of our work, our meals, and our play. If we are going to increase our endurance, we must increase the power of our heart and blood vessels, as well as that of our muscles. The real thing to be trained in the gymnasium and on the athletic field is the heart rather than the muscles.
Fortunately, however, the heart is itself a muscle, alive and growing, and with the same power of increasing in strength and size that any other muscle has. So that up to a proper limit, all these things which throw strain upon the heart in moderate degree, such as running, working, and thinking, are not only not harmful, but beneficial to it, increasing both its strength and its size. The heart, for instance, of a thoroughbred race-horse is nearly twice the size, in proportion to his body weight, of the heart of a dray-horse or cart-horse; and a deer has more than twice as large a heart as a sheep of the same weight.
The important thing to bear in mind in both work and play, in athletic training, and in life, is that this work must be kept easily within the powers of the heart and of the other muscles, and must be increased gradually, and never allowed to go beyond a certain point, or it becomes injurious, instead of beneficial; hurtful, instead of helpful. Over-work in the shop or factory, overtraining in the gymnasium or on the athletic field, both fall first and heaviest upon the heart.
Importance of Food, Air, and Exercise. At the same time, the system must be kept well supplied through the stomach with the raw material both for doing this work and for building up this new muscle. When anyone, in training for an event, gets "stale," or overtrained, and loses his appetite and his sleep, he had better stop at once, for that is a sign that he is using more energy than his food is able to give him through his stomach; and the stomach has consequently "gone on a strike."
How to Avoid Heart Overstrain and Heart Disease. The way, then, to avoid overstrain and diseases of the heart and blood vessels is:—
First, to take plenty of exercise, but to keep that exercise within reasonable limits, which, in childhood, ought to be determined by a school physician, and in workshops and factories by a state factory physician.
Second, to take that exercise chiefly in the open air, and as much of it as possible in the form of play, so that you can stop whenever you begin to feel tired or your heart throbs too hard—in other words, whenever nature warns you that you are approaching the danger line.
Third, to
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