Pathologic Hematopoiesis: Congenital dyserythropoietic anemia Type II, congenital erythrocytosis anf thrombocytopenias

The blood contains several different types of cells. Each of these cell types is quite distinct in appearance, and each has a specific biological function. Despite their extreme structural and functional differences, blood cells are the progeny of a single type of cell: the hematopoietic stem cell (HSC). The processes involved in the production of the various cell types of the blood from the HSCs are collectively called hematopoiesis. Hematopoiesis includes HSC self-renewal, HSC commitment to specific lineages, and maturation of lineage-committed progenitors into functional blood cells. Self-renewal may occur by symmetric HSC division, such as expansion of the HSC pool during fetal life or post-HSC transplantation. Other possible fates of HSC divisions include apoptosis or mobilization to the peripheral circulation following stress such as growth factor stimulation or depletion of marrow cells by irradiation or chemotherapy. During normal steady state conditions, HSCs reside mainly in the marrow cavity, but under certain stress conditions HSCs can migrate and colonize other organs like liver and spleen in a process termed extramedullary hematopoiesis. Hematopoiesis begins early during embryogenesis and undergoes many changes during fetal and neonatal development. Unlike some organ systems that form in early life and are not continually replaced, turnover and replenishment of the hematopoietic system continue throughout life.

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