Bone Marrow

one of the largest organs in the body
confined to the upper ends of the femur and humerus, sternum, clavicles, scapulae, ribs, vertebrae, cranium and pelvis.
volume of haemopoietically active bone marrow in an adult around 1-2 litres
can expand by several-fold to meet increased needs.
During excessive demand for blood cell production e.g. in chronic haemolytic anaemias such as thalassaemia foci of haemopoietic tissue may arise outside the bone marrow in the liver, spleen or other sites (extramedullary haemopoiesis). Clinically, the expansion of extramedullary haemopoietic masses may cause complications by compression of neighbouring structures.
highly organised organ composed of haemopoietic cells, fat cells and vascular structures, surrounded by bony tissue.
haemopoietic progenitor cells continually replenish the peripheral blood cell populations.