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Reticulocytes and mature [[Erythrocytes|erythrocytes]] leave the [[Bone Marrow - Anatomy & Physiology|bone marrow]] by ‘squeezing’ through the capillary endothelial cells. Precursors to these stages cannot change shape and therefore remain confined to the bone marrow.
Reticulocytes and mature [[Erythrocytes|erythrocytes]] leave the [[Bone Marrow - Anatomy & Physiology|bone marrow]] by ‘squeezing’ through the capillary endothelial cells. Precursors to these stages cannot change shape and therefore remain confined to the bone marrow.
Reticulocytes are immature RBCs released from normal bone marrow in increased numbers in response to anaemia. Although the nucleus has been lost, these cells still have ribosomal RNA in their cytoplasm for continued haemoglobin synthesis. Ribosomal RNA appears as blue granules when stained with new methylene blue. Cells showing polychromasia are reticulocytes but not all reticulocytes are polychromatic. In dogs a polychromatophil is a reticulocyte. In cats two types of reticulocytes are recognised, aggregate and punctate. Feline aggregate reticulocytes have distinctly clumped RNA and a 12 hour life span; these mature into punctate reticulocytes with only a few scattered granules of RNA, which have a 10-12 day life span in blood. Less mature RBCs, with a retained nucleus, may circulate in response to severe regenerative anaemias; these are usually metarubricytes although earlier cells may be seen. (NW)
==Development==
==Development==