Mature red cells are one of the few cellular structures in the human body that begin as nucleated cells and become anucleate. This remarkable development takes place in the bone marrow over a period of 5 days as each precursor cell goes through three successive divisions, yielding smaller and more compact red cells.1 Several features of the red cell change dramatically: the cell size reduces, the nucleus:cytoplasm (N:C) ratio reduces, nuclear chromatin becomes more condensed, and the cytoplasm color is altered as hemoglobinization becomes more prominent (Table 3.1). In the bone marrow, erythrocytes at various stages of maturation seem to cluster in specific areas, the so-called erythroblastic island, easily identified in the bone marrow aspirate by the tell-tale morphological clues of erythropoiesis— extremely round nuclear material, combined with basophilic cytoplasm. The main site of adult erythro-poiesis is the bone marrow located in the sternum and iliac crest, whereas erythropoiesis in children takes place in the long bones and sternum.
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