Chapter 45 Hematopoiesis and Hematopoietic Failure
 Hematopoiesis : is the process of formation and development of blood cells from pluripotent
hematopoietic stem cell
 Hematopoietic Tissues:
 Hematopoiesis commences in the embryonic yolk sac, in which early erythroblasts in blood islands
form the first hemoglobinized cells.
 After 6 weeks’ gestation, the fetal liver begins producing primitive lymphocytoid cells,
megakaryocytes, and erythroblasts, and the spleen becomes a secondary site of erythropoiesis.
 Hematopoiesis then shifts to its definitive long-term site in the bone marrow, the principal site for
lifelong hematopoiesis in the normal host.
 Early in life, all fetal bones contain regenerative bone marrow, but the marrow becomes progressively
replaced by fat with age.
 In adults, active marrow resides only in the axial skeleton (i.e., sternum, vertebrae, pelvis, and ribs)
and in the proximal ends of the femur and humerus.
 Note :Bone marrow samples are taken from iliac crest or sternum.