bone marrow (bone MAYR-oh)

The soft, sponge-like tissue in the center of most bones. It produces white blood cells, red blood cells, and platelets.

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Anatomy of the bone; drawing shows spongy bone, red marrow, and yellow marrow. A cross section of the bone shows compact bone and blood vessels in the bone marrow. Also shown are red blood cells, white blood cells, platelets, and a blood stem cell.