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Encyclopedia > Erythropoiesis

Erythropoiesis is the process by which red blood cells (erythrocytes) are produced. In human adults, this usually occurs within the bone marrow; in humans with certain diseases, in fetuses and in some animals, erythropoeiesis also occurs outside the bone marrow, within the spleen, liver, or yolk sac. This is termed extramedullary erythropoiesis.

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

In the process of red blood cell maturation, a cell undergoes a series of differentiations. A pluripotent stem cell becomes a multipotent stem cell, in turn becoming a unipotential stem cell, a pronormoblast, a basophilic normoblast, a polychromatophilic normoblast, and orthochromatic normoblast, a reticulocyte, at which point the cell is released from the bone marrow, and ultimately becomes an erythrocyte or mature red blood cell circulating in the peripheral blood. These stages correspond to specific appearances of the cell when stained with Wright's stain and examined by light microscopy, but correspond to other biochemical changes.

In the process of maturation a basophilic pronormoblast is converted from a cell with a large nucleus and a volume of 900Ám3 to an enucleated disc with a volume of 90Ám3.

A feedback loop involving erythropoietin helps regulate the process of erythropoiesis, so that, in non-disease states, the production of red blood cells is equal to the destruction of red blood cells and the red blood cell number is sufficient to sustain adequate tissue oxygen levels but not so high as to cause sludging, thrombosis, or stroke. Erythopoeitin is produced in the kidney in response to low oxygen levels. In addition, erythropoeitin is bound by circulating red blood cells; low circulating numbers lead to a relatively high level of unbound erythropoeitin, which stimulates production in the bone marrow.

See also

  • Anemia: a condition with an abnormally low level of red blood cells
  • Polycythemia: a condition with an abnormally high level of red blood cells

  Results from FactBites:
UMDNJ Research Fall 2004--Adrenergic modulation of erythropoiesis following trauma (1024 words)
Erythropoiesis and the formation of red blood cells is a complex process involving bone marrow stem cells, progenitor cells, and stromal cells.
It is the impact of this stress or "adrenergic state" on erythropoiesis and its subsequent dysfunction that is the focus of my research.
Adrenergic modulation of erythropoiesis is known to occur under normal conditions and typically red blood cell growth is enhanced.
BioMed Central | Full text | Neonatal erythropoiesis and subsequent anemia in HIV-positive and HIV-negative Zimbabwean ... (6440 words)
For the present study, we used a model of the relationships between indicators of iron status and erythropoiesis (Figure 1) to guide our examination of erythropoiesis in young infants and the impact of HIV infection on the process.
Transferrin receptors (TfRs) present on the surface of erythroid cells increase with the expansion of the erythroid mass, and a soluble truncated form of the tissue receptor increases proportionally in the serum [15-17].
A noteworthy effect of HIV infection on erythropoiesis was the modification of infant infection on the association between ferritin and TfR at 6 months of age.
  More results at FactBites »



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