Hematopoietic bone marrow (red marrow), light micrograph. Red blood cells are situated inside the sinusoid capillaries (vascular compartment). Surrounding the capillaries is the cellular hematopoietic compartment of the bone marrow, where the blood cell precursors are located. The largest cells are megakaryocytes. There are also some adipocytes (fat cells). They become more predominant with age, converting red marrow in yellow marrow.