PH
Although bones appear lifeless, they contain living cells, blood vessels, and nerves. These cells constantly repair tiny cracks, remove old tissue, and build new bone.
Bone marrow inside many bones also produces millions of blood cells every second. Without these living processes, the skeleton would quickly become weak. Every bone is far more active than it appears from the outside. The skeleton is a living organ, not just a frame.
© National Institutes of Health