MEDizzy - A 65-year-old slightly cyanotic male presents to his

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Physiology of the Hematopoeitic and Lymphoreticular Systems

A 65-year-old slightly cyanotic male presents to his physician complaining of pruritis and nose bleeds. A blood test reveals a hematocrit of 62, leading to the diagnosis of polycythemia vera. Treatment includes aspirin to prevent thromboses and periodic phlebotomy to reduce the hematocrit. The reduction in hematocrit is beneficial because it does which of the following?

ExplanationPolycythemia vera is a disease in which an abnormally large number of red blood cells are produced. The large number of red blood cells causes an increase in blood viscosity by two or three times normal. Patients with polycythemia vera often have high blood pressure (because of increased blood volume) and cyanosis (because of increased oxygen extraction from blood flowing slowly through capillaries). In primary polycythemia vera, there is a primary bone marrow etiology. In secondary polycythemia vera, increased erythropoietin production occurs secondary to hypoxia (chronic obstructive pulmonary disease [COPD], high altitude), smoking (due to carboxyhemoglobin), or renal cell carcinoma.