The red blood cells (RBCs) are also called erythrocytes, which are spherical in shape with a depression in the middle to impart maximum surface area to the cells. The greater the surface area the more they are able to capture oxygen. RBCs get their red colour from oxygenated iron-rich protein haemoglobin. Hence the arteries are depicted by red colour. Haemoglobin is a pigment that binds oxygen and forms oxyhaemoglobin. These cells have an average life of about 120 days.
White blood cells (WBCs or leucocytes) are the transparent and colourless cells. They are larger in size and fewer in number than red cells. The main function of the white cells is producing antibodies to defend the body against infection and disease. The white cells are referred as the soldier’s body. The count of WBCs increases when there is an infection in the human body. These cells have amoeba-like movement, due to which these cells can reach the infected parts of the body.
The thrombocytes or blood platelets are the smallest cells in the body, about one-third size of the red blood cells. Thrombocytes play an important role in the clotting of blood and control of bleeding after injury. In case of injury, these platelets gather in large numbers immediately and plug the injured cavity by attaching at the site and to one another. Platelets occupy a much smaller fraction of the volume of the blood.