Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

Leukocytes, or white blood cells, function as a defense against invading microorganisms. The totalwhite blood cell count (WBC) is normally 5,000-10,000 per cu. mm. of blood, but may increase to veryhigh levels in cases of infection or as a reaction to treatment by radiation and/or chemotherapy.There are several types of white blood cells. The relative percentages of the various cells found inblood is called the white cell differential (see Book 5, Abstracting a Medical Record).Leukocytes are produced in the bone marrow and in lymphoid tissue. Granulocytes (granularleukocytes), lymphocytes and monocytes (agranular leukocytes or mononuclear leukocytes) originatein the bone marrow, but multiply in the lymphoid tissue.Platelets (thrombocytes) are formed in the bone marrow by fragmentation of large cells(megakaryocytes). Platelets normally number 200,000 to 500,000 per cu. mm. of blood. Upondisintegration they release a substance, thromboplastin, which combines with blood proteins andcalcium to form prothrombin which initiates the production of fibrin to form blood clots (coagulation).Sometimes a blood clot will form within the heart or blood vessels partially or totallyobstructing the vessel. Such a blood clot is called a thrombus. When a thrombus is dislodged andmoves to another location, it is called an embolus (thromboembolus).119