<P> The blood vessels of the bone marrow constitute a barrier, inhibiting immature blood cells from leaving the marrow . Only mature blood cells contain the membrane proteins, such as aquaporin and glycophorin, that are required to attach to and pass the blood vessel endothelium . Hematopoietic stem cells may also cross the bone marrow barrier, and may thus be harvested from blood . </P> <P> The red bone marrow is a key element of the lymphatic system, being one of the primary lymphoid organs that generate lymphocytes from immature hematopoietic progenitor cells . The bone marrow and thymus constitute the primary lymphoid tissues involved in the production and early selection of lymphocytes . Furthermore, bone marrow performs a valve - like function to prevent the backflow of lymphatic fluid in the lymphatic system . </P> <P> Biological compartmentalization is evident within the bone marrow, in that certain cell types tend to aggregate in specific areas . For instance, erythrocytes, macrophages, and their precursors tend to gather around blood vessels, while granulocytes gather at the borders of the bone marrow . </P> <P> Animal bone marrow has been used in cuisine worldwide for millennia, such as the famed Milanese Ossobuco . </P>

The formed elements in the blood are produced in both yellow bone marrow and red bone marrow