Extrusion of the nucleus from the late erythroblast gives rise to the reticulocyte which enters the peripheral blood. Reticulocytes may be identified by traces of cytoplasmic RNA that can be stained with methylene blue or acridine orange.


The reticulocyte count is a useful index of erythropoiesis. Reticulocytes constitute about 1% of the total circulating red cells, are slightly larger than red cells and evolve into mature red cells in several days.


The main functions of red cells are to transport oxygen to the tissues and carbon dioxide to the lungs. Another major function is the acid/base buffering effect of the hemoglobin.


At the end of their life-span, red cells are phagocytosed by macrophages in the liver, spleen and bone marrow, which are the principal sites for the destruction of senescent red cells.


Whilst the iron and proteins from the hemoglobin are recycled, the heam is metabolised into various pigmented compounds and excreted by the liver and the kidney.