344 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. Leukemia Leukemia is a cancer of the blood that causes the bone marrow to produce abnormal, cancerous white blood cells. These cancerous WBCs multiply uncontrollably and grow larger than normal WBCs, but they lack the infection-fighting ability of normal WBCs. Cancerous white blood cells have a negative impact on bone marrow, which leads to decreased production of RBCs, WBCs, and platelets. Leukemia is classified as either acute or chronic. Acute leukemia worsens quickly, while chronic leukemia progresses more slowly. Children with leukemia usually have acute leukemia. Adults may contract either acute or chronic leukemia. There are four types of leukemia. Two types are acute and two are chronic. • Acute lymphocytic leukemia (ALL): ALL is characterized by an overproduction of lymphocytes. It is most common in children under the age of 15 years but may also occur in adults over age 45. ALL is the most common type of cancer in children. • Acute myeloid leukemia (AML): AML develops when the bone marrow produces too many myeloblasts, or immature WBCs. Myeloblasts ultimately develop into neutrophils, eosinophils, and basophils. It is the most common form of leukemia in adults. • Chronic lymphocytic leukemia (CLL): Like acute lymphocytic leukemia, CLL is characterized by extremely high levels of lymphocytes. CLL is rare in children and most often affects middle-aged adults. • Chronic myeloid leukemia (CML): In CML, the bone marrow manufactures too many granulocytes (neutrophils, eosinophils, and basophils). People with chronic leukemia may not experience any symptoms, sometimes even for years after they develop the disease. By comparison, people with acute leukemia often seek medical care because they feel sick. Symptoms of both chronic and acute leukemia include weakness, fever, bone and joint pain, and stomach swelling and pain from an enlarged spleen or liver. People with leukemia also have frequent infections because their abnormal WBCs are unable to aid in the immune response. marrow sensitivity to erythropoietin, causing even more RBCs to be produced. High RBC counts cause blood to become more viscous, increasing the likeli- hood of blood clot formation. Polycythemia is diagnosed by testing hemoglobin or hematocrit levels. Unusually high levels of hemoglobin or hematocrit indicate excessive RBC production. Phlebotomy, the process of drawing or removing blood from the body, is the standard treatment for polycythemia. Phlebotomy reduces the number of RBCs circulating in the body. This helps correct hematocrit levels. Aspirin has also been used to treat polycythemia because it prevents excess clotting, but aspirin therapy is not advised for anyone with a history of spontaneous bleeding or stroke. Intravascular Clotting Normally, due to the body’s anticoagulating and fibrinolytic mechanisms, blood clots do not form in an unbroken vessel. However, sometimes blood clots do form in an intact blood vessel, usually a vein. This intravascular clot is called a thrombus. The clot may dissolve on its own, but if it remains in the vessel and becomes large enough, it may cause a blockage that results in damage to or death of the tissue supplied by that vessel. For instance, a blockage in a coronary artery could result in a heart attack. If the clot becomes dislodged from the vessel wall and is transported in the bloodstream it is called an embolus. An embolus floating in the bloodstream that enters a smaller diameter artery could cut off blood flow to an organ. When an embolism blocks blood flow to the lungs, it is called a pulmonary embolism, and it is potentially fatal. Intravascular clots may develop due to a roughening of the endothelium of the vessel resulting from trauma, atherosclerosis, severe burns, or infection. The roughened endothelial lining leads to platelet aggregation and clot formation. Clots may also occur when blood flows too slowly and clotting factors accumulate, allowing clot formation. Risk factors for clot formation include pregnancy, individuals over 60 years of age, or sitting for long periods of time like on a flight or after surgery. Therapy for intravascular clots includes aspirin or use of an anticoagulant such as heparin or Coumadin.