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Erythropoiesis (view source)

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Erythrocyte stem cells contain no haemoglobin and it is only after several cell divisions that pro-erythrocyte haemoglobin starts to be generated within the cells. When the haemoglobin levels are at the correct concentration the nucleus reduces in size and is removed from cell. Cells at this stage still have ribosomes and other organelles and stain differently to mature erythrocytes; they are known as '''reticulocytes'''. After a few days these mature having reached a final haemoglobin concentration of 34%.

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'''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. References: [[NationWide Laboratories]]

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.

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EPO is transported from kidneys to [[Bone Marrow - Anatomy & Physiology|bone marrow]] where it acts upon receptors on the CFU-E’s and causes differentiation into erythrocyte precursors. It also increases the rate of division and maturation of developing erythrocyte precursors by increasing the rate of gene transcription. Thus it is not the number of [[Erythrocytes|erythrocytes]] but the oxygen concentration that controls erythrocyte numbers. EPO release can be affected by any form of renal pathology. Inflammatory induced release of interleukins reduces the secretion of erythropoietin.

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The mechanism of oxygen concentration detection is via HIF-1 (hypoxia inducible factor 1) which is a transcription activator that is oxygen sensitive.

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The mechanism of oxygen concentration detection is via HIF-1 (hypoxia inducible factor 1) which is a transcription activator that is oxygen sensitive.

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~~== References ==~~

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~~Reticulocytes: [[NationWide Laboratories]]~~

[[Category:Haematopoiesis]]

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