The Heart-Pump and Its Pipe-Line System : The Heart

A Handbook of Health
by Woods Hutchinson

(Page 14 of 30)

Structure and Action of the Heart. Now what is it that keeps the blood whirling round and round the body in this wonderful way? It is done by a central pump (or more correctly, a little explosive engine), with thick muscular walls, called the heart, which every one knows how to find by putting the hand upon the left side of the chest and feeling it beat. The heart is really a bulb, or pouch, which has ballooned out from the central feed pipe of the blood supply system, somewhat in the same way that the stomach has ballooned out from the food tube.

The walls of this pouch, or bulb, are formed of a thick layer of very elastic and powerful muscles almost as thick as the palm of your hand. When the great vein trunk has poured blood into this pouch until it is swollen full and tight, these muscles in its walls shut down sharply and squirt or squeeze the blood in the heart-pouch into the great artery-pipe, the aorta. In fact, you can get a very fair, but rough, idea of the way in which the heart acts by putting your half-closed hand down into a bowl of water and then suddenly squeezing it till it is shut tight, driving the water out of the hollow of your hand in a jet, or squirt.

"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?"

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.

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.

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.

Houghton Mifflin Company
Copyright, 1911, By Woods Hutchinson
All Rights Reserved
Tenth Impression

About the Author

Woods Hutchinson (1862-1930) was an American physician, born at Selby, Yorkshire, England. He graduated from Penn College, Oskaloosa, Iowa, in 1880 and received his medical degree from the University of Michigan four years later. He worked as a professor of anatomy at the State University of Iowa and then became a professor of comparative pathology at the University of Buffalo.