Blood transports food and oxygen to all living cells in the body, and takes away waste matter from them. Blood consists mainly of a watery liquid called plasma. Red cells, white cells and platelets float in the plasma. The disc-shaped red blood cells take oxygen from the lungs to the tissues. White blood cells help to fight infection by attacking harmful bacteria.
Small particles called platelets are important for blood clotting.
There are approx. 500 red cells to each white one. A red blood cell lives for about 120 days after it enters the bloodstream. When blood dies, the cells are disposed of by the liver and the spleen. The bone marrow continuously makes new blood cells to replace the dead cells.