<unk>  or leukocytes are<unk>  of the immune system<unk> hich defend the body against both infectious disease and foreign materials. Several different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent<unk> in the bone marrow known as a hematopoietic stem<unk>  Leukocytes are found throughout the body, including the blood and lymphatic system.
The number of leukocytes in the blood is often an indicator of disease. There are normally between 4×109 and 11×109<unk>  in a litre of blood, making up approximately 1% of blood in a healthy adult. In conditions such as leukemia the number of leukocytes is higher than normal, and in leukopenia this number is much lower. The physical properties of leukocytes, such as volume, conductivity, and granularity, may change due to activation, the presence of immature<unk> , or the presence of malignant leukocytes in leukemia.
White blood cells
Granulocyte
Blood cell
Red blood cell
Oocyte
Lymphocyte
Cell 
Platelet