Blood cells play essential roles in oxygenation of tissues, coagulation, protection against infectious agents, and tissue repair. Blood cell deficiency is a relatively common occurrence that can have profound repercussions. The most common cause of erythrocyte deficiency, or anemia, is insufficient supply of iron, vitamin B12, or folic acid, substances required for normal production of erythrocytes. Pharmacologic treatment of these types of anemia usually involves replacement of the missing substance. An alternative therapy for certain types of anemia and for deficiency in other types of blood cells is administration of recombinant hematopoietic growth factors, which stimulate the production of various lineages of blood cells and regulate blood cell function.
|dTMP synthesis||A set of biochemical reactions that produce deoxythymidylate (dTMP), an essential constituent of DNA synthesis. The cycle depends on the conversion of dihydrofolate to tetrahydrofolate by dihydrofolate reductase (Figure 33–1)|
|G-CSF||Granulocyte colony-stimulating factor, a hematopoietic growth factor that regulates production and function of neutrophils|
|GM-CSF||Granulocyte-macrophage colony-stimulating factor, a hematopoietic growth factor that regulates production of granulocytes (basophils, eosinophils, and neutrophils), and other myeloid cells|
|Hemochromatosis||A condition of chronic excess total body iron caused either by an inherited abnormality of iron absorption or by frequent transfusions to treat certain types of hemolytic disorders (eg, thalassemia major)|
|Megaloblastic anemia||A deficiency in serum hemoglobin and erythrocytes in which the erythrocytes are abnormally large. Results from either folate or vitamin B12 deficiency anemia|
|Microcytic anemia||A deficiency in serum hemoglobin and erythrocytes in which the erythrocytes are abnormally small. Often caused by iron deficiency|
|Neutropenia||An abnormally low number of neutrophils in the blood; patients with neutropenia are susceptible to serious infection|
|Pernicious anemia||A form of megaloblastic anemia resulting from deficiency of intrinsic factor, a protein produced by gastric mucosal cells and required for intestinal absorption of vitamin B12|
|Thrombocytopenia||An abnormally low number of platelets in the blood; patients with thrombocytopenia are susceptible to hemorrhage|
Iron and Vitamin Deficiency Anemias
Microcytic hypochromic anemia, caused by iron deficiency, is the most common type of anemia. Megaloblastic anemias are caused by a deficiency of vitamin B12 or folic acid, cofactors required for the normal maturation of red blood cells. Pernicious anemia, the most common type of vitamin B12 deficiency anemia, is caused by a defect in the synthesis of intrinsic factor, a protein required for efficient absorption of dietary vitamin B12, or by surgical removal of that part of the stomach that secretes intrinsic factor.
Other Blood Cell Deficiencies
Deficiency in the concentration of the various lineages of blood cells can be a manifestation of a disease or a side effect of radiation or cancer chemotherapy. Recombinant DNA-directed synthesis of hematopoietic growth factors now makes possible the ...