bloodforming

Bloodforming, more commonly termed hematopoiesis, is the process by which the cellular components of blood are produced, developed, and maintained. In humans, it begins during embryogenesis and continues throughout life. In the fetus, sites include the yolk sac, liver, and spleen; after birth, the bone marrow becomes the primary hematopoietic organ, with remnants in the liver and spleen in some conditions.

Hematopoiesis starts with hematopoietic stem cells (HSCs) that reside in the bone marrow. These self-renewing cells give rise to multipotent progenitors that differentiate into two major lineages: the lymphoid lineage (producing B cells, T cells, and NK cells) and the myeloid lineage (giving rise to erythrocytes, megakaryocytes/platelets, granulocytes, and monocytes). Erythropoiesis involves production of red blood cells and is regulated mainly by erythropoietin; megakaryopoiesis yields platelets; granulopoiesis produces neutrophils, eosinophils, and basophils; monocytopoiesis and lymphopoiesis generate monocytes and lymphocytes, respectively.

Bloodforming activity is regulated by a network of growth factors and cytokines, including erythropoietin, thrombopoietin, granulocyte–macrophage colony-stimulating factor, interleukins, and stem cell factors, acting in concert with transcription factors to guide lineage commitment and maturation. Disorders of hematopoiesis include anemia, leukemias, myelodysplastic syndromes, and other marrow failures. Therapies such as iron supplementation, cytokine therapy, and bone marrow or stem cell transplantation aim to restore effective hematopoiesis.