eritroblast

An eritroblast, also known as a nucleated red blood cell or normoblast, is an immature red blood cell precursor found in the bone marrow. It develops from a hemocytoblast and progresses through several stages of maturation, characterized by changes in nuclear size and chromatin appearance, as well as the synthesis of hemoglobin within the cytoplasm. These stages are typically categorized as proerythroblast, basophilic erythroblast, polychromatophilic erythroblast, and orthochromatophilic erythroblast.

During maturation, the nucleus of the erythroblast shrinks, and its chromatin becomes progressively condensed. Simultaneously, the cytoplasm, initially basophilic due to abundant ribosomes for protein synthesis, gradually becomes eosinophilic as hemoglobin accumulates. The final stage, the orthochromatophilic erythroblast, ejects its nucleus to become a reticulocyte, which then enters the bloodstream and matures into an erythrocyte (mature red blood cell).

The presence of eritroblasts in the peripheral blood, outside of the bone marrow, is generally considered abnormal and can indicate various pathological conditions. For instance, their presence may be a sign of increased red blood cell production in response to anemia, or it could suggest bone marrow infiltration by tumors or other diseases. The number and type of eritroblasts observed in a blood smear can provide valuable diagnostic information to clinicians.