=== Leukocytes (white blood cells) ===

Leukocytes are divided into two major types: the granulocytes and the agranulocytes. The white blood cells are involved in inflammatory and immune reactions and function both within and outside of the bloodstream. In different disease states a marked increase in numbers of leukocytes above the normal range is called leukocytosis (10,000 or more per cu. mm) whereas a decrease below 5000 per cu. mm is called leukopenia.