Which part in a body forms living cells and platelets required for the existence of human beings?

In the human adult, the bone marrow (the soft fatty tissue inside bone cavities), produces all of the living cells which include red blood cells, 60-70 percent of the white cells (i.e., the granulocytes), and all of the platelets. In total, it produces about 95% of the body's blood cells. Most of the adult body's bone marrow is in the pelvic bones, breast bones, and the bones of the spine.

Bone marrow contains young parent cells called stem cells. These blood-forming stem cells can grow into all 3 types of blood cells - red cells, white cells, and platelets. These blood- forming stem cells make copies of themselves, and they also produce mature blood cells. When blood cells are fully mature and functional, they leave the bone marrow and enter the blood.

Normal blood cells lasts for a limited time (ranging from a few hours to a few days for white blood cells, to about 10 days for platelets, to about 120 days for red blood cells) and must be replaced constantly. When the oxygen content of body tissues is low or the number of red blood cells decreases, the kidneys produce and release erythropoietin, a hormone that stimulates the bone marrow to produce more red blood cells. The bone marrow produces and releases more white blood cells in response to infections. It produces and releases more platelets in response to bleeding. Aging has some effect on bone marrow and blood cells, resulting in less cell-producing marrow.