When Does Extramedullary Hematopoiesis Occur?

Extramedullary hematopoiesis in fetus is a physiological process which consists of two steps: (1) primitive hematopoiesis which develops in yolk sack during 2.5–8 weeks of fetal life as a temporary red cell forming system, and (2) definitive hematopoiesis which is developed later to generate the entire blood cells and ...

What is extramedullary hematopoiesis and where does it occur?

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; during this time the main site of fetal hematopoiesis are liver and the spleen.

How does extramedullary hematopoiesis occur?

Extramedullary hematopoiesis occurs early in fetal development and also plays important roles in adult life. Hematopoiesis occurs in the fetal liver and spleen. Hematopoietic stem and progenitor cells in the fetal liver migrate to the bone marrow and the marrow becomes the major hematopoietic site after birth.