Erythropoiesis

The tibia and femur cease to be important sites of hematopoiesis by about age 25; the vertebrae, sternum, pelvis and ribs, and cranial bones continue to produce red blood cells throughout life.

[5] Comparison of erythrocyte production by marrow stem cell lines from old and young adult donors shows no significant differences.

[6] This finding implies that little or none of the proliferative capacity of the erythropoietic stem cells is exhausted by a lifetime of normal functioning.

[6] In the process of red blood corpuscle maturation, a cell undergoes a series of differentiations.

Lack of either causes maturation failure in the process of erythropoiesis, which manifests clinically as reticulocytopenia, an abnormally low amount of reticulocytes.

Recent studies have also shown that the peptide hormone hepcidin may play a role in the regulation of hemoglobin production, and thus affect erythropoiesis.

Iron must be released from macrophages in the bone marrow to be incorporated into the heme group of hemoglobin in erythrocytes.

The secretion of hepcidin is inhibited by another hormone, erythroferrone, produced by erythroblasts in response to erythropoietin, and identified in 2014.

If there is no systemic feedback inhibition, for example, the diminishment or absence of suppressors of cytokine signaling proteins, giantism may result as shown in mice models.

[10][11] In addition to the steady state erythropoiesis, acute anemia probably stimulates another response which results in rapid development of new red blood cells.