The blood which flows through our body contains many different materials and cells. Each part of the blood has its own special job to do. The liquid part of our blood is called the plasma and makes up a little more than half the blood. It is light yellow in colour and thicker than water as many substances are dissolved in it. These substances are protein, antibodies that fight disease, fibrinogen that helps the blood to clot, carbohydrates, fats and salts, in addition to the blood cells themselves.
The red cells (also called red blood corpuscles) give the blood its colour. There are so many of them in the blood that it makes it all look red. There are about 35 trillion of these tiny, round, flat discs moving around in your body all at once.
As the young red cell grows and takes on adult form in the marrow, it loses its nucleus and builds up more and more haemoglobin.
Haemoglobin is the red pigment, or colour. Red cells live only for about four months and then are broken up, mostly in the spleen. New red cells are always being formed to replace the cells that are worn out and destroyed.
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Heart rate is the number of times that the heart actually contracts in a minute. You can measure this yourself by finding the pulse in your wrist, then gently holding your finger on it and counting the number of beats per minute.
