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WHAT IS THE HEART ? "Go to your bosom Knock there and ask your heart What it doth know" ....William Shakespeare.

The heart is the symbol of life. Without a heart, a human being cannot live. It is also a symbol of love - we say a man has given his heart away in love. The heart also stands for courage - we talk about being lion-hearted. It also indicates joy and happiness - as in being a hearty soul. In medical terms, the heart is the pump that provides energy to the rest of the body.

HOW THE HEART IS BUILT.... To work, to play, to do anything at all, the human body needs energy. This energy is provided by blood, which runs within arteries and veins. The body draws fuel in the form of chemicals and oxygen from the blood, and turns it into energy for work. At the same time, the waste materials produced in the body are dumped in the blood to be carried away and destroyed in other areas. There are two kinds of blood vessels (or tubes) in the body. ARTERIES carry "pure" or "red" blood from the heart to the other organs, and VEINS bring back "impure" or "blue" blood to the heart to be purified.

For blood to carry out this work, it must circulate, or go around and around in the arteries and veins. It needs to be pumped. The HEART is the pump, which makes blood travel to every part of the body.

The human heart is a hollow organ, roughly the size of your clenched fist, shaped like an upside-down pear and weighs around 11 ounces (or 300 grams)(ADULT). It is made up of muscle, just like the muscle in your arms and legs. But, when you walk or work for a long time, your arm and leg muscles get tired, and you need to rest. Heart muscle is a little different, because it does not get tired. And that is lucky, because if the heart stopped, life could not continue. The heart's structure makes it an efficient, never-ceasing pump. On an average, the heart contracts and relaxes about 70 to 80 times per minute without you ever having to think about it.

In this picture, you can see the red "aorta", the blue "superior vena cava", the purple "right atrium", the pink "ventricles" and the brown "pulmonary artery".

In the heart, there are four chambers - just like the rooms of a house. The upper chamber is called an ATRIUM. There are two upper chambers, one on the right and one on the left. The lower chamber is called a VENTRICLE. Again, there are two ventricles, right and left.

The flow of blood in a particular pattern through the heart chambers and arteries and veins is called the CIRCULATION. To make this easy to understand, let's take a little trip. Imagine yourself to be in a little boat, sailing in the blood stream .

Let's begin our trip from the veins. These carry the "impure" blood (or "blue" blood), into which all the wastes of the body have been dumped. As you float down the veins, you would first reach the upper heart chamber on the right side - the RIGHT ATRIUM. The atrium is a kind of store room. Here, you would wait for a short time, while more blood collects until the atrium is full.

Then you would flow into the right lower chamber - the RIGHT VENTRICLE. The ventricle, unlike the atrium, is a powerful pump. Suddenly, and forcefully, you will be propelled into a narrow tunnel, called the PULMONARY ARTERY. This is a tube that carries the "impure" blood to the LUNGS.

In this picture, the right sided portion of the heart alone is colored blue.

The lungs are like bellows or balloons in the chest. There are two lungs, one on each side of the chest. When you breathe, air enters the lungs.

When "impure, blue" blood enters the lung, it mixes with the air you breathe in. OXYGEN (a gas in the air you breathe that makes life possible) enters the blood and the "impurities" leave it. The blood is now "pure" or "bright red" as it leaves the lungs.

As you leave the lungs, you will come back to the heart. But this time, it is to the LEFT upper chamber that you return - the LEFT ATRIUM. After a short wait here, again, you would be guided into the left lower chamber - the LEFT VENTRICLE.

The left ventricle is the strongest chamber of the heart. It is the part of the heart that will pump blood to the rest of the body. The pressure that is produced in the left ventricle is similar to that in a garden hose when the water is turned on full-blast.

So, when you are in the left ventricle, suddenly you would get a powerful thrust and enter another tube (or artery). This artery is the AORTA - the largest and toughest artery in the whole body. From the aorta, "pure" blood, carrying oxygen and energy-giving nutrients, is distributed to all organs of the body.

In this picture, you see the left sided heart structures colored red.

Blood flows to the brain, and you can think, see, dream - and read this article ! It flows to the stomach and intestines, and you digest the food you ate today. Blood flows to your hand and leg muscles, and you can write and walk and run. Each and every part of the body gets energy from the blood to do its special kind of work.

This picture shows a "diagrammatic" image of the circulation of blood in arteries and veins. The pure arterial blood is colored red, while the impure venous blood looks blue.

So, let's put it all in a nutshell. "Impure" blood from veins reaches the right atrium of the heart, then flows to the right ventricle. From here, it passes through the pulmonary artery to the lungs, where oxygen is taken up, and wastes destroyed. The "pure" blood reaches the left atrium, and then the left ventricle. From here, it is powerfully pumped into the aorta, from which it is directed to all the parts of the body.

Why doesn't it flow backwards ?

The answer: Because there are VALVES to keep blood flowing in the same direction. A valve is something like a door. But while you can go both in and out of a door, a valve will only let you in ! You can't get out through the same valve.

There are FOUR VALVES in the human heart, one at each junction of two chambers. Between the right atrium and right ventricle, there is the TRICUSPID VALVE. It is called tricuspid because it has three leaves or `cusps'. From the right ventricle, blood is kept flowing towards the lungs by the PULMONARY VALVE. In between the left atrium and left ventricle there is another one called the MITRAL VALVE. Some imaginative anatomist saw that it looked like the bishop's `miter', and so gave it this name ! Finally, the junction of left ventricle and aorta is guarded by the AORTIC VALVE. Both the aortic and pulmonary valves have `cusps' or leaves that are half-moon shaped, and they are fancifully called the SEMI-LUNAR VALVES !

HOW DOES THE HEART WORK ? The heart is a kind of machine to pump blood. Like any machine, it too needs fuel to work. This fuel is provided by the blood. How does this happen ?

Blood from the left ventricle enters the aorta. The very first branches from the aorta are small "feeder" arteries called CORONARY ARTERIES. These arteries turn back to run over the heart itself. There are two main coronary arteries, the right and left. These main coronary arteries give rise to several smaller branches which then dive into the heart muscle. They bring vital nutrients and oxygen to the heart. Using these nutrients, the heart can perform its pumping action.

So how is this conversion into pumping action done ? The heart, is a muscle, but with some special features. The muscle is formed by millions of small CELLS. Cells are like bricks; row upon row of cells, arranged in different patterns, make up all human organs. The cell in heart muscle (called a MYOCYTE) is made up of two types of protein - called ACTIN and MYOSIN. These proteins, using the energy from oxygen and nutrients, slide over each other in a special way that causes the whole muscle to shorten. The muscle cells are arranged in a circular pattern, like a ball or a balloon. When the muscle shortens, the heart becomes smaller - its like squeezing a balloon filled with water. Blood from inside the chambers is then pumped out with some force.


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