Changes

[[Erythrocytes|Erythrocytes]] contain no nucleus and are thus only produced from stem cells. During the fetal stage production is in both the [[Liver - Anatomy & Physiology|liver]] and [[Spleen - Anatomy & Physiology|spleen]] however production is transferred to the [[Bone Marrow - Anatomy & Physiology|bone marrow]] ([[Bone Marrow - Anatomy & Physiology#Red marrow|red marrow]]) in the final stages of gestation. Initially erythropoiesis occurs in all bones, however after puberty production is limited to membranous bones (ribs, vertebrae, pelvic bones etc.) as the long bones contain adipose tissue in place of red marrow.

[[Erythrocytes|Erythrocytes]] contain no nucleus and are thus only produced from stem cells. During the fetal stage production is in both the [[Liver - Anatomy & Physiology|liver]] and [[Spleen - Anatomy & Physiology|spleen]] however production is transferred to the [[Bone Marrow - Anatomy & Physiology|bone marrow]] ([[Bone Marrow - Anatomy & Physiology#Red marrow|red marrow]]) in the final stages of gestation. Initially erythropoiesis occurs in all bones, however after puberty production is limited to membranous bones (ribs, vertebrae, pelvic bones etc.) as the long bones contain adipose tissue in place of red marrow.

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. Reticulocytes contain some RNA and continue to produce haemoglobin. After a few days these mature having reached a final haemoglobin concentration of 34%.

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%.

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 confoned 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.  

==Development==

==Development==

Production of [[Erythrocytes|erythrocytes]] is regulated by '''erythropoietin''' (EPO) which is produced in the yolk sac, [[Liver - Anatomy & Physiology|liver]] and kidney from embryonic life until early neonatal life. In the adult it is produced only in the kidneys. Erythropoietin is a glycoprotein hormone and is controled by a negative feedback mechanism. Normal levels are low with sufficient amounts to maintain a basal level of new erythrocyte production. If blood oxygen concentration falls, the release of erythropoietin rises.

Production of [[Erythrocytes|erythrocytes]] is regulated by '''erythropoietin''' (EPO) which is produced in the yolk sac, [[Liver - Anatomy & Physiology|liver]] and kidney from embryonic life until early neonatal life. In the adult it is produced only in the kidneys. Erythropoietin is a glycoprotein hormone and is controled by a negative feedback mechanism. Normal levels are low with sufficient amounts to maintain a basal level of new erythrocyte production. If blood oxygen concentration falls, the release of erythropoietin rises.

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 the developing erythrocyte precursors by increasing gene transcription. Thus it is not the number of [[Erythrocytes|erythrocytes]] but the oxygen concentration that regulates its release. EPO release can be affected by any form of renal pathology.

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.

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

Erythropoietin production is directly and indirectly (via regulatory genes) increased by HIF-1 (Hypoxia inducible factor 1) which is a transcription activator that is oxygen sensitive.

Inflammatory induced release of interleukins reduces the secretion of erythropoietin.

[[Category:Haematopoiesis]]

[[Category:Haematopoiesis]]