Introduction to Hematology
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Hematology is the study of the normal and pathologic aspects of blood and blood elements. Blood is a very unique fluid composed of many cellular elements as well as a liquid portion consisting of proteins, amino acids, carbohydrates, lipids, and other macromolecules and low-molecular-weight precursors. The hematopoietic system is characterized by high cell turnover and replenishment throughout one’s life. The pluripotent hematopoietic stem cell (HSC) is the progenitor for all cells that arise in blood. The cellular elements that arise from this stem cell include red blood cells, white blood cells, and platelets. Normal white blood cells in the peripheral circulation include neutrophils, monocytes, eosinophils, basophils, and lymphocytes. Since the HSC also gives rise to cells of the lymphoid system, the study of hematology also includes the lymph nodes and lymphoid tissue. There is no specific organ for hematologic disorders, and its diseases arise within the bone marrow, the lymph nodes, or the intravascular compartment. The latter includes the endothelial cells lining blood vessels and the proteins in the blood plasma. The circulating cell-endothelial cell interface and the rheologic aspects of blood coursing through the intravascular compartment also influence “hematology” and its many parts.