Hematopoietic

Hematopoietic refers to the formation and development of the cellular components of blood. Hematopoiesis describes the continuous production of erythrocytes, leukocytes, and platelets from hematopoietic stem cells, which reside in the bone marrow in adults. The process maintains blood cell numbers and functions in health and adapts to varying physiological demands.

Within the hematopoietic system, hematopoietic stem cells (HSCs) are multipotent and capable of self-renewal. They give rise to progenitors that differentiate along two main lineages: the myeloid lineage, which produces red blood cells, platelets, and most white cells (neutrophils, monocytes, eosinophils, basophils), and the lymphoid lineage, which forms T cells, B cells, and natural killer cells. Maturation occurs in specialized microenvironments and is guided by cytokines and growth factors.

Sites and development: during embryogenesis, hematopoiesis begins in the yolk sac, then shifts to the fetal liver and spleen before settling in the bone marrow at birth or shortly thereafter. In some conditions, hematopoiesis can occur outside the marrow (extramedullary hematopoiesis), such as in the liver or spleen. Clinical relevance includes bone marrow failure disorders, leukemias, and other myeloid or lymphoid diseases.

Clinical applications and therapy include bone marrow or peripheral blood stem cell transplantation, donor matching, and graft-versus-host disease risk. Treatments frequently rely on cytokines (for example erythropoietin, thrombopoietin, G-CSF, GM-CSF) to stimulate or modulate hematopoiesis. Ongoing research aims to expand HSCs, correct genetic defects, and treat hematologic diseases.