Extramedullary haematopoiesis

Extramedullary hematopoiesis (EMH or sometimes EH) refers to hematopoiesis occurring outside of the medulla of the bone (bone marrow).It can be physiologic or pathologic. Extramedullary hematopoiesis (EMH or sometimes EH) refers to hematopoiesis occurring outside of the medulla of the bone (bone marrow).It can be physiologic or pathologic. Physiologic EMH occurs during embryonic and fetal development mainly. It has been done in many different locations, depending on the moment or the kind of hematopoiesis that is needed in that moment. Pathologic EMH can occur during adulthood when physiologic hematopoiesis can't work properly in the bone marrow and the hematopoietic stem cells (HSC) have to migrate to other tissues in order to continue with the formation of blood cellular components. Pathologic EMH can be caused by myelofibrosis, thalassemias or disorders caused in the hematopoietic system. During fetal development, hematopoiesis occurs mainly in the fetal liver followed by localization to the bone marrow. Hematopoiesis also takes place in many other tissues or organs such as the yolk sac, the aorta-gonad mesonephros (AGM) region, the spleen, and lymph nodes.