noun, plural: hematopoieses
Hematopoiesis is the process of forming new blood cellular elements in vertebrates. The process starts at the stem cells becoming committed progenitor cells that eventually develop into fully mature differentiated cells in the blood. In humans, the cellular elements of the blood include red blood cells, white blood cells, and thrombocytes. These cells are all derived from the multipotent hematopoietic stem cells (HSCs). These have the ability to give rise to different mature blood cell types, such as erythrocytes, T cells, B cells, granulocytes, megakaryocytes, macrophages, and dendritic cells.
During embryonic development in humans and other mammals, hematopoiesis initially occurs in the yolk sac (particularly, blood islands). The process then occurs at the spleen, liver, and lymph nodes as the embryo further develops. In fetus, it occurs primarily in the liver. When bone marrow is formed, hematopoiesis will occur chiefly in this site till adulthood. In children, it occurs mainly in the bone marrow of femur and tibia. In adults, it will occur mainly in cranium, vertebrae, sternum, and pelvis. Furthermore, the maturation (and sometimes, the proliferation) of lymphoid cells will take place in the lymph nodes, thymus, and spleen. Extramedullary hematopoiesis is when the process resumes in the liver, spleen, and thymus. In other vertebrates, hematopoiesis occurs in the gut, the spleen, the kidney, or in where there is a loose stroma of connective tissue and slow blood supply.1
Based on the cell type that differentiates at the end of the developmental process, hematopoiesis may be referred to as follows:
Word origin: Ancient Greek haima ("blood") + poiesis ("to make")
- hemopoiesis (or haemopoiesis)
- hematopoietic (adjective)
1 Zon, L. I. (1995). "Developmental biology of hematopoiesis". Blood. 86 (8): 2876–91.