1 Answer

duckie 1118 in a nutshell bone marrow produces new blood cells.    This is what Wikipedia has to say about it:     (the answer to your specific question is in the last sentence of this paragraph).

Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. Bone marrow is also a vital element of the lymphatic system, as it produces lymphocytes and acts to prevent the backflow of lymph. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg (143 lbs), bone marrow accounts for approximately 2.6 kg (5.7 lbs). The bone marrow hematopoietic compartment produces approximately 500 billion cells per day that use the bone marrow vasculature as a conduit to the systemic circulation.^[1]