Blood Cells and Platelets

There are 3 main types of blood cells- erythrocytes, leucocytes and platelets.


Erythrocytes (Red blood cells)

These are disc shaped cells with no nucleus, and are produced in the red bone marrow by hematopoietic cells. There are over 5 million of these cells in 1mm3 of blood. These cells are used to transport oxygen around the body in the form of oxyhaemoglobin – Oxygen molecules combined with the haemoglobin molecules found in the red blood cells. This happens because haemoglobin is a protein and contains iron. The iron readily combines with oxygen. There are over 250 million haemoglobin molecules in one red blood cell.

Red blood cells are made very quickly as they do not live for very long (approximately 4 months). Of course, their short life span is due to a lack of nucleus. Old red blood cells are broken down in the liver, spleen and bone marrow. The haemoglobin present in old red blood cells may be reused or turned into bile and excreted.

Leukocytes (White blood cells)

These are the body’s defence mechanism and are produced in the bone marrow as well as the lymph nodes. These cells are used to destroy and eliminate germs that enter the human body. How? They can ‘squeeze’ out through the walls of blood capillaries into all parts of the body. There are about 10 thousand of these cells for every 1mm3 of blood. They are irregular in shape and have a large nucleus which is sometimes lobed.

The diagram below shows a comparison between the white blood cells and the red blood cells.


These are small cell fragments which are used in the clotting mechanism. Blood clotting is important as it prevents entry of germs and materials when a wound is formed. It also prevents further escape of blood. They have no nucleus and are also made in the red bone marrow.

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