In an adult human body there are about 5.5 litres of blood. These litres form the most amazing transportation system imaginable. The blood circulates through the body so that it reaches every one of the billions of cells that make up the body tissues. It brings food and oxygen to each cell, carries away waste products, carries hormones and other chemical substances, helps the body fight infection, and helps regulate body heat.
The blood is made up largely of colourless liquid called "plasma", and it is the red corpuscles floating in this liquid that give blood its red colour.
It is when we consider how many of these blood cells there are in the ten pints of blood that our imagination is staggered. There are about 25 billion of them! In a single drop of blood there are some 300,000,000 red corpuscles. If the cells were joined together in a chain, keeping their actual size, the chain would go four times around the earth.
Even though the cells are tiny, they have a tremendous surface area. For instance, if you could weave them into a carpet, the total surface area of this carpet would be 4,090 square meters. Since at any one given moment one-quarter of the blood is to be found in the lungs, about 1,000 square meters of blood-cell surface are constantly being exposed to the air. Every second, 2 billion blood cells pass by the air chambers of the lungs!
Because the air in lowland regions is under greater pressure, it contains more oxygen than at high altitudes. So the higher up a person lives, the higher is the number of blood cells he has. A person living in the mountain regions of Switzerland may have 50 per cent more blood cells than one living in London. High blood pressure involves a great many older people. It is believed that 15 to 20 per cent of all deaths in the United States in people over fifty years of age is due to high blood pressure!
The blood is made up largely of colourless liquid called "plasma", and it is the red corpuscles floating in this liquid that give blood its red colour.
It is when we consider how many of these blood cells there are in the ten pints of blood that our imagination is staggered. There are about 25 billion of them! In a single drop of blood there are some 300,000,000 red corpuscles. If the cells were joined together in a chain, keeping their actual size, the chain would go four times around the earth.
Even though the cells are tiny, they have a tremendous surface area. For instance, if you could weave them into a carpet, the total surface area of this carpet would be 4,090 square meters. Since at any one given moment one-quarter of the blood is to be found in the lungs, about 1,000 square meters of blood-cell surface are constantly being exposed to the air. Every second, 2 billion blood cells pass by the air chambers of the lungs!
Because the air in lowland regions is under greater pressure, it contains more oxygen than at high altitudes. So the higher up a person lives, the higher is the number of blood cells he has. A person living in the mountain regions of Switzerland may have 50 per cent more blood cells than one living in London. High blood pressure involves a great many older people. It is believed that 15 to 20 per cent of all deaths in the United States in people over fifty years of age is due to high blood pressure!
