Patient is a 7-year-old girl who was brought to her physician by her mother with complaints of general fatigue, anorexia, and unexplained bruises and "rash" for the past 2 weeks. Current status: P.D.'s vital signs are: temperature, 98.6°F; heart rate, 92; blood pressure, 90/60; respirations, 18; and height and weight in the 55th percentile. Her skin is warm, pale, and dry, with bruising on the extremities and trunk. Examination of the skin reveals small petechial lesions on the arms and legs. There is no hepatosplenomegaly. There are three palpable, nontender lymph nodes in the submaxillary chain. Laboratory data: Hgb, 8.8; Hct, 26; RBC, 3.1 million; WBC, 45,000 with 10% blasts; and platelets, 50,000. A bone marrow aspiration, lumbar puncture, and other studies revealed acute lymphoblastic leukemia (ALL). 1. What cell type is abnormal in ALL? 2. Identify the clinical signs that suggest she has leukemia and provide a physiologic rationale for each sign. 3. Review the given laboratory data and relate each finding to leukemia and explain why each finding occurs in this disease.