Every human being has a heart that pumps blood throughout his body. This is absolutely necessary, because blood carries the oxygen taken from the lungs, and all the digested foods that have been eaten, to the tissues. Without oxygen, nourishing sugars, and proteins and fats, our organs could not possibly work or live.
Did you ever place your ear against someone’s chest and listen to the heartbeat? Do it, and you will hear a sound like thub-dub each time the heart beats. A child’s heart beats about eighty to ninety times a minute, while a grown-up’s heart beats somewhat slower.
The heart is made of a special kind of muscle that contracts and relaxes automatically, without our having to do anything about it. You might think the heart is shaped like the pictures on a candy box or a Valentine’s Day card, but it really isn’t. The actual shape of the heart is shown in the diagram. It is about the size of an orange in a child, and of a small grapefruit in a grown-up.
The heart, commonly believed to be on the left side, is actually more toward the center of the chest and even extends over into the right side. It is surrounded on three sides by the lungs.
Blood from the body flows to the right side of the heart and is pumped to the lungs to get oxygen. It then flows to the left side of the heart and is pumped throughout the rest of the body.
The heart is hollow on the inside and has four parts. The two chambers on the right side receive blood that has already traveled to all the tissues of the body. This blood is a dark reddish purple color. This dark blood is then pumped by the heart through large vessels, called arteries, to the lungs where it picks up a new oxygen supply. The oxygen then turns the blood a bright red color. It is then returned from the lungs to the left side of the heart. The heart then pumps the blood from its two chambers on the left side into the largest artery in the body, the aorta. The aorta connects with smaller arteries throughout the body. After the blood delivers its oxygen and its vitamins and chemicals and nourishing food elements to each and every part of the body, veins then carry the blood back again to the right side of the heart. Once the blood is carried through the veins back to the heart, the whole process is repeated over again.
How much blood do you think a boy or girl has? Well, take a look at the quart container of milk and imagine that there are three of them. That’s about how much blood, three quarts, each of you has. Your mother may have about five quarts of blood and your father, because he is bigger, about six quarts.
The heart is one of the most remarkable organs in the body. It beats about 12,000 times a day, whether you’re asleep or awake. And each clay, it pumps your three quarts of blood through your body about 3,000 times!
Just as we take good care of our teeth by brushing them regularly and visiting our dentist every few months, we must also do what is good for our heart. You remember that regular exercise keeps the muscles of the arms and legs good and strong. Well, the heart is a muscle too, and we keep it strong by playing and exercising regularly. If we sit around and do nothing all day, sooner or later the heart won’t work as well as it should. Also, if you get fat from overeating, your heart will get fat, too, and that’s not good for your health.
When you run and play, your heart beats fast and hard and pumps your blood more rapidly through your body. Sometimes, when you run very fast for a long time, you can hear your heart beating and pounding in your chest. This is healthy, for it exercises the heart muscles and helps keep them strong. Sometimes, when you get frightened your heart beats fast, too, but. this can’t hurt you. As soon as you realize there’s nothing to be afraid of, your heart slows down to normal.
When you rest or sleep, your heart beats more slowly. It rests too. The next time you go to your doctor, ask him if you can listen to your own heart through his stethoscope. You will actually be able to hear your heart pump your own blood. Here are some rules to follow to help keep your heart healthy:
1. Run and play and exercise regularly.
2. Don’t eat too much, so you don’t get fat.
3. Stay in bed as long as your doctor tells you to when you are sick. 4. Don’t let yourself get overtired from playing too hard.
5. Eat all the good things your mother tells you to.
6. Get at least eight to ten hours of sleep each night.
The Arterial and Venous Systems. Blood is propelled by the contractions of the heart through the various arteries to the tissues of the body. The pulse is an indication of these contractions, which are transmitted along the arterial system. There is no pulse in the venous system, blood is returned to the heart by the force of gravity and by the pressure transmitted The arteries that carry the blood from the heart to all the organs have a smooth inner lining, so the blood can flow quickly over it, and walls containing small muscles that can contract and relax, so the blood can be pushed along without stopping. When the muscles in the walls of the arteries contract, the blood is pushed along The capillaries are very small blood vessels that directly nourish the body cells.
The arterioles carry blood from the arteries and the venues carry It toward the veins faster. When the muscles in the walls of the arteries relax, the blood flows more slowly. This action causes a pulse. You can feel the pulse yourself by placing your fingers on your own wrist or temple, or more easily, by feeling someone else’s wrist or temple. The pulse you feel means that the heart has just beaten, or contracted, pumping the blood faster through the artery.
Very often when you see the doctor, he will feel your pulse and look at his watch while holding your wrist. He is ting how fast your pulse is beat Generally, when you have a fever feel sick, your pulse beats much faster than usual.
At the same time as the blood tiers all its nourishment to the tissues, picks up waste materials that will Fentually be gotten rid of by your body. For example, as the tissues use oxygen, they give back carbon dioside to the blood. And when the sugar yes been used by your tissue cells, lacticiteid and other waste chemicals are even back. These substances are carjed to the heart through the veins. The lams, like the arteries, have a smooth peer lining, but their walls have much muscle tissue. As a result, veins can’t contract like arteries. The blood in the veins gets back to the heart by being pushed along from behind by the pumping action of the heart. Imagine a whole line of freight trains being pushed along the tracks by an engine p the back. The engine is like the heart, and the trains way up front are Ue the blood in your veins.
The arteries get smaller and smaller as they extend into the tissues until they hecome tiny, tiny little passage
ways only big enough for a few blood cells to pass through at one time. These tiny blood vessels are called capillaries. They surround all of our tissues, and it is through these capillaries that the blood gets to every single part of the body. Then, after the blood has supplied the tissues and picked up the waste, it goes back into tiny, tiny veins. As the veins go back toward the heart, they get bigger and bigger.
The flowing of the blood through the heart, the arteries, the capillaries, and the veins is called the circulation. To keep our circulation in good working order we must move about and exercise a lot. Sitting still in front of the television set all clay is not the proper way to take care of our circulation. But we shouldn’t put a strain on our circulation, either, by being so active that we don’t get enough rest and sleep.