Erythropoese

Erythropoese, also known as erythropoiesis, is the process by which red blood cells are produced from hematopoietic stem cells. It ensures the continual replacement of mature erythrocytes that have a limited lifespan, and it is tightly regulated by signals that respond to the body's oxygen needs.

In adults, erythropoiesis occurs primarily in the red bone marrow of the axial skeleton and major long bones. During development, the liver and spleen contribute to red cell production. The process is driven by erythropoietin, a hormone mainly produced by the kidneys in response to hypoxia, which stimulates survival, proliferation, and differentiation of erythroid progenitors.

The differentiation sequence starts with a common erythroid progenitor and progresses through distinct stages: proerythroblast (pronormoblast), basophilic erythroblast (rubriblast), polychromatophilic erythroblast (rubricyte), and orthochromatic erythroblast (metarubricyte). Nuclei are progressively condensed and eventually expelled from orthochromatic erythroblasts, forming reticulocytes that enter the circulation. Reticulocytes mature into erythrocytes within about one to two days in the bloodstream.

Adequate erythropoiesis requires iron availability for hemoglobin synthesis, as well as vitamin B12 and folate for DNA replication during cell division. The erythroblastic island niche, organized around a central macrophage, supports late-stage erythroid development and iron recycling.

Clinically, impaired erythropoiesis can lead to anemia, while excessive production can cause polycythemia. Reticulocyte counts and erythropoietin levels are commonly used to evaluate disorders of red cell production. Therapeutic erythropoietin is employed for certain anemias, such as those associated with chronic kidney disease or chemotherapy.