How does Blood Move Through the Body?

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How does the blood travel in our body? Information on pumping cycle of heart and blood circulation in human body.

Heart Diagram

The blood system is called the circulatory system because the blood travels in circuits, or paths that go all the way around the body. All the blood that goes out to one part, such as an arm, comes back and then go es out again to the same part or another part. So the blood is used over and over again in the body many, many times. The circulatory system includes five different kinds of parts: (1) the blood, (2) the heart, (3) the arteries, (4) the capillaries, and (5) the veins. The blood carries various materials to and from all living cells as it flows around the body. Also, the heart pumps the blood and makes it flow to all parts of the body. The blood tubes, or blood
vessels, through which it Hows out from the heart and back again are the arteries, the capillaries, and the veins.

We often use some kind of pump when we want to make water flow through pipes. The pump that makes blood flow through your blood vessels is your heart. Your body contains only about 5 or 6 quarts of blood. But every day about 4000 gallons of blood are pumped through your heart. Sometimes the heart puts out as much as 8 gallons of blood a minute, while at other times it puts out only about 1 gallon a minute. Even then, in about a minute and a half the heart is pumping as much blood as there is -in the entire body. The heart can make the blood flow so fast because its walls are made of thick, heavy muscles. This special kind of muscle tissue is found only in the heart. When these muscles relax, blood flows into the heart. When the muscles contract, blood is forced out of the heart.

The two sides of the heart are separated by a partition down the middle. So blood on one side of the heart cannot cross over to the other side. Each side of the heart has two rooms, or chambers. The upper one is the receiving chamber, or auricle, while the lower one is the pumping chamber, or ventricle. A valve lets blood flow from each auricle into the ventricle below it but keeps the blood from flowing back. Another valve lets the blood out of each ventricle but keeps the blood from coming back into the heart.

Actually, the heart is two pumps, side by side. Here is what happens during one heartbeat, or single stroke of this double pump. Suppose that the heart muscles are relaxed. Veins bring blood to the right side of the heart from all parts of the body except the lungs. This blood goes into the right auricle and then into the right ventricle. Other veins bring different blood to the left side of the heart from the lungs. This blood goes into the left auricle and then into the left ventricle. Now the heart muscles contract, and the valves between the auricles and ventricles close. The blood in the right ventricle is forced into the pulmonary artery and carried the lungs. The blood in the left ventricle is forced into another big artery, called the aorta and carried to all other parts of the body.

The heart pumps blood into the blood vessels. The blood is forced through these tubes in all parts of the body and then flows back through them to the heart. The blood vessels that carry blood from the heart are the arteries, while those that bring blood back to the heart are the veins. The capillaries are found near the cells in all parts of the body. There is hardly a place in the body thicker than a hair that does not have some of these tiny blood vessels. It would take about 2000 capillaries placed side by side to make an inch. So they are much too small to be seen with the naked eyes. Through the very thin walls of the capillaries, dissolved materials can pass from the blood to the cells and back into the blood.
Circulatory System
Each drop of blood goes out of the heart through in artery, flows through some capillaries, and then comes back to the heart again through a vein. Only two big arteries leave the heart: the pulmonary artery and the aorta. But the larger
arteries divide and subdivide to form smaller arteries. They branch again and again until they reach every part of the body. At one end, the capillaries spread out from a little artery. At the other end, they come together into a little vein. The small veins join to form larger veins. Then fue larger veins come together into a few big veins that return to the heart.

When blood comes back to the heart from any part of the body except the lungs, it goes into the right side of the heart and then to the lungs. But when blood comes back to the heart from the lungs, it goes into the left side of the heart and then to the rest of the body. So every drop of blood goes through the lungs each time it makes a round trip through the body. This is called a double circulation. The blood that comes back to the heart from most of the body contains much carbon dioxide. Nearly all of its oxygen has been used by the cells. Before this blood is sent back through the body again, it must first give up much of the carbon dioxide and then get a new supply of oxygen. So the heart pumps the used blood through the lungs, where carbon dioxide is given out and oxygen taken in. When the renewed blood goes back to the heart, it is ready for recirculation. One side of the he art pumps only blood that is high in oxygen, while the other side pumps only blood that is high in carbon dioxide. The partition between the two sides of the heart keeps the used blood with its carbon dioxide from being sent back through the body until it has given up much of its carbon dioxide and renewed its supply of oxygen.

All the important organs of the body must be well supplied with blood. Blood must be carried to the bones, muscles, skin, and brain to supply them with food and oxygen. Blood must be sent to the small intestine to get digested food. Blood must also go to the kidneys to have nitrogen wastes taken out. To supply all the organs, the heart pumps blood that comes from the lungs into the aorta. Just after this big artery leaves the heart, small branches turn back into the heart muscles to provide the cells with food and oxygen. A short distance from the heart, large branches of the aorta are sent up into the head and arms. The main artery then turns downward. One large branch goes to the digestive organs, and two other large branches enter the kidneys. At the lower end of the abdomen, the large artery divides inlo two smaller ones. One of these goes into each leg. All along the large artery are many smaller branches that carry blood to various parts. In this way, every part of the body gets the food and oxygen that it needs from the blood.

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