Pluripotent stem cell: undifferentiated cell which divides and differentiates into 3 main hematopoietic lineages, i.e. erythropoiesis, myelopoiesis and thrombopoiesis.
Erythropoiesis: is organised into clusters known as erythroblastic islands (erythrons) which are dispersed in the intertrabecular space. They do not normally occur peritrabecularly.
Myelopoiesis: immature myelopoietic cells (myeloblasts and promyelocytes) are localised in the peritrabecular space, more mature granulopoietic cells (myelocytes, metamyelocytes, segments and rods) are situated closer to the centre of the intratrabecular space. Normal M:E (myeoloid-to-erythroid ratio) is approx. 2 – 3:1.
Thrombopoiesis: 3 – 5 separate megakaryocytes (thromocyte precursors) are usually sparsly dispersed in one field of view with 400× magnification ratio.
Bone marrow also produces monocytes and lymphocytes.
Other marrow cells: Other marrow cells form the microenvironment that is suitable for hematopoiesis; they include stromal cells i.e. adipocytes, osteoblasts and osteoclasts, fibroblasts, macrophages (a Fe supply), endothelial cells (forms vascular sinuses), and also lymphocytes, mast cells and plasma cells.