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.
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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.
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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.
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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.
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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.
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