The blood flows like a river in the body through the blood vessels. It is called the river of life, because it supplies the cells of the body with the materials they need for nourishment and repair, and it removes wastes from cells.
In addition, the blood contains cells that fight diseases and substances that repair damaged parts of the body.
Almost everyone has had a cut or injury that caused bleeding. The red liquid that flows out of a cut is blood.
There are between five and six litres of blood in the body of an average adult. Blood varies in colour depending upon the amount of oxygen it carries. Blood us bright red when it contains a high level of oxygen. It is dark, brownish red after giving up its oxygen to the cells of the body.
Parts of the blood
Blood gas two main parts. Plasma is the liquid part of the blood. The other part is made up of blood cells.
The solid parts of the blood are the red blood corpuscles (red blood cells), white blood corpuscles (white blood cells)and platelets. Corpuscles is the Latin word for “little body.”
Red corpuscles and what they do
This contain haemoglobin, which is a compound of iron. This chemical can combine very well with oxygen from the air in our lungs.
It us task of red blood corpuscles to carry oxygen to the cells in all parts of the body and upon reaching these cells, to give up the oxygen in them. When haemoglobin combines with oxygen, it turns bright red. That is why blood which is running out of a cut is always red.
White corpuscles and what they do
Diseases are caused by large numbers of bacteria in our body. It is the function of the white corpuscles to destroy bacteria and to protect you from disease.
To destroy a bacterium, a white blood dell lives over to the bacterium and then engulfs it (swallows it by surrounding it with it’s cytoplasm).
Platelets and what they do
Platelets cause blood to clot: thus they help to stop bleeding. They release a chemical substance whenever there is an injury. The substance together with other chemicals in the blood forms a mass of fibres.
These fibres are insoluble in the plasma and form a clot which plugs (closes) the wound, thus preventing the loss of more blood. The final clot consists of threads of fibrin among which are trapped blood cells.
Plasma and what they do.
We have seen that plasma is the liquid part of the blood. About 90% of the plasma is water. Digested food, minerals and various chemicals and certain proteins are dissolved in the plasma. Plasma is sticky and straw coloured.
If someone suffers from a severe loss of blood, called a haemorrhage, resulting from a wound or internal injury, the lost blood had to be replaced or death may result. The process of transferring blood into a person is called transfusion.
The blood of the receiver should be similar to the donor’s type of blood, otherwise it may lead to death.
Usually, careful cross matching of blood is done before blood transfusions are given.