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The Heart

In the diagram below the
red arrows indicate deoxygenated blood
and the
blue arrows indicate oxygenated blood.

Drawing of the heart © Shirley Burchill

The mammalian heart has four chambers - two atria (singular: atrium) and two ventricles. There is a quick and effective way to draw a diagram of the heart.

1. Draw a straight pencil line down the centre of the page

Heart drawing 

2. Now draw parallel lines on both sides of this first line, about one centimetre away from it. These lines should reach from the top of the first line to about two thirds of the way down it.

Heart drawing 

3. Next draw the side outlines for the right and the left.

Heart drawing 

4. Now give these walls some thickness. The atria walls are thin, the right ventricle wall is thicker than the atria walls. The wall of the left ventricle should be made thicker than the right.

Heart drawing 

5. Now add the valve flaps and the cords.

Heart drawing 

6. Make your diagram less angular by curving the ends of the arteries. You can also put the semi-lunar valves in position.

Heart drawing 

Now label the different parts of the heart. Add arrows to show the direction of the blood flow. Use two different colours – one for blood rich in oxygen (oxygenated blood) and the other for blood low in oxygen (deoxygenated blood).

You can see from the diagram that there are two main arteries connected to the heart. The aorta carries oxygenated blood to the body. The pulmonary artery carries deoxygenated blood to the lungs and it is the only artery to carry deoxygenated blood. There are two veins associated with the heart. The vena cava, or great vein, carries deoxygenated blood back to the heart from the body. The pulmonary vein is the only vein to carry oxygenated blood which is on its way to the heart from the lungs.

The diagram also shows you that the right and side of the heart, both atrium and ventricle, contains only deoxygenated blood. This blood moves through the heart on its way to the lungs where it picks up oxygen and releases carbon dioxide. The left hand side of the heart contains only oxygenated blood which has come from the lungs and is destined to be distributed throughout the body.

When the heart pumps blood the cycle starts with the two atria contracting together. This pushes the blood into the ventricles. The two ventricles then contract at the same time. The blood cannot return into the atria because the valves are held shut. The blood is therefore directed into the arteries for distribution. The left ventricle has a thicker wall than the right ventricle because it has more cardiac muscle in it. It is this ventricle which has to provided the push for the blood to reach all parts of the body. The right ventricle pushes the blood to the lungs which are close by the heart in the thorax.

Heart Disease

Although the heart is pumping blood through its auricles and ventricles it still needs to have its own blood supply. These blood vessels are called the coronary vessels and they are found throughout the cardiac muscle.

When you look at the model of the heart you can see some of the coronary arteries and veins. The arteries, as we have seen, have thick walls and smaller spaces for the blood to travel through. Sometimes deposits of substances, such as cholesterol, stick to the walls of an artery and make the space which the blood flows through even smaller. If these deposits grow then the blood will have trouble getting through the artery. When blood stops moving it clots (coagulates). If this happens in an artery then the blood does not reach the local capillary system. This means that the cardiac muscle cells do not receive oxygen and can no longer function. The result of this is a heart attack. If the blocked artery is a smaller artery, supplying a small capillary system, then the heart attack can be mild. If, however, the artery is one of the larger cardiac arteries which is supplying blood to smaller arteries and a larger section of the capillary system, then the heart attack is likely to be much more serious and possible fatal.

People who are overweight and eat a diet containing a lot of animal fat are more likely to suffer from heart attacks. Nicotine from cigarettes, cigars and pipe tobacco also causes deposits to form in arteries and is one of the major causes of heart attacks amongst smokers.

Not smoking, plenty of exercise and a healthy diet reduces the chances of heart disease.

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