Orthochromatophilic erythroblast, reticulocyte and mature erythrocytes

The orthochromatophilic erythroblast represents the last stage in the erythroid series with nucleated cells. The cytoplasm is more eosinophilic due to the loss of ribosomes and the additional accumulation of hemoglobin. The nucleus is small, round and very heterochromatic. The cell eventually extrudes its nucleus forming the reticulocyte.

The reticulocyte is the cell formed after the orthochromatic erythroblast extrudes its nucleus. The slight basophilia of the cell is due to the presence of polyribosomes that can still synthesize hemoglobin. Special stains used to demonstrate reticulocytes cause the polysomes to clump and form a reticulated pattern, hence the name of these cells.

After reticulocytes are released into the blood stream, their ribosomes and remaining cytoplasmic organelles are rapidly degraded, forming mature erythrocytes. Erythrocytes have a distinctive biconcave disc shape that maximizes surface-to-volume ratio, which facilitates gas exchange.