Blood is made of clear liquid called plasma and three types of cells: red blood cells, platelets and white blood cells.

All blood cells come from the same type of cell, known as stem cells. Early on, they develop into either myeloid or lymphoid cells.

• Myeloid cells include all red blood cells, platelets and the white blood cells that are known as granulocytes and monocytes.
• Lymphoid cells include all other white blood cells, known as lymphocytes.

Red blood cells collect oxygen from your lungs and carry it to all parts of your body. If you don’t have enough red blood cells you have anaemia. Anaemia can make you look pale, may cause headaches and make you feel tired, dizzy and irritable.

Platelets are needed to help your blood to clot following an injury. A reduced number of platelets may cause prolonged bleeding or easy bruising.

White blood cells play a major role in the body’s defence against infection. A decrease in white blood cells puts you more at risk of getting infections.

Blood cells are made in bone marrow, the spongy part in the centre of your bones.

When the body is healthy, the numbers of red cells, white cells and platelets in the blood are kept in balance. Diseases of the blood cells, like leukaemia, can cause this balance to be thrown out.



Leukaemia
Leukaemia is cancer of blood-forming cells. Leukaemia causes large numbers of immature white blood cells to be produced.

These abnormal cells, called leukaemia blasts, can’t carry out the normal functions of white blood cells. They crowd the bone marrow and spill into the blood and may then spread into organs such as the liver, spleen, lungs and kidneys. Occasionally, they may also spread into the fluid surrounding the brain and spinal cord.

Because there are so many abnormal white cells crowded into the bone marrow, the marrow can’t make enough normal red blood cells, white blood cells and platelets.

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