hæmatopoiesis

Hæmatopoiesis is the biological process by which all blood cells are formed, produced, and differentiated from hematopoietic stem cells (HSCs). These multipotent stem cells reside primarily in the bone marrow of adult vertebrates, although in embryos they are found in the yolk sac, liver, and spleen before migrating to the marrow. HSCs can self‑renew and give rise to three primary lineages: myeloid, erythroid, and lymphoid.

The myeloid lineage generates granulocytes (neutrophils, eosinophils, basophils), monocytes, megakaryocytes (the precursors of platelets), and erythrocytes. The erythroid lineage exclusively produces red blood cells, while the lymphoid lineage produces B cells, T cells, and natural killer cells. Differentiation proceeds through a series of committed progenitors, each marked by specific surface proteins and transcription factors such as GATA‑1, PU.1, and c‑Myb. Cytokines and growth factors—erythropoietin, granulocyte‑macrophage colony‑stimulating factor, and interleukins—regulate proliferation, differentiation, and survival at each stage.

Regulation of hæmatopoiesis is tightly controlled by a feedback loop responsive to oxygen levels, infection, and blood loss. Oxygen sensing by erythropoietin production in the kidneys stimulates red cell production, whereas mobilization of HSCs from marrow to peripheral blood occurs during inflammation or physical stress.

Clinical disorders of hæmatopoiesis include aplastic anemia, myelodysplastic syndromes, leukemia, and polycythemia vera. Therapeutic approaches often target specific stages of differentiation, such as transfusions, bone marrow transplantation, or molecular inhibitors of abnormal signaling pathways. Understanding hæmatopoiesis remains essential for developing treatments for blood diseases and for improving regenerative medicine strategies.