The macrophage is part of the bone marrow stroma. They constitute about of nucleated bone marrow cells (myelogram). They arise from monocytes. They phagocytose and remove cellular debris in the bone marrow. For this reason, they contain iron, lipids and nuclear debris. Histiocyte is another commonly used synonym for macrophage.



Macrophages have a bright, round to oval nucleus which often shows nucleoli as well as ample pale blue cytoplasm, whose limits are not always clearly recognizable. Numerous dark blue granules that correspond to phagocytized debris or siderosomes is typical.