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 a few cell divisions that pro-erythrocyte haemoglobin starts to enter 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 called 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. Reticulocytes contain some RNA and continue to produce haemoglobin. 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. Precursor to these stages cannot change shape and therefore remain in the [[Bone Marrow - Anatomy & Physiology|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 confoned to the [[Bone Marrow - Anatomy & Physiology|bone marrow]].

==Development==

==Development==