It is easy to picture bone as dead, dry material — like the bones you see in a museum display. In a living body, bone is the opposite: it is a living connective tissue, full of blood vessels and living cells, that is constantly being broken down and rebuilt throughout your life. Specialised cells called osteoblasts build new bone, while other cells called osteoclasts break old bone down, and the two stay in balance to keep bone strong and appropriately shaped for the loads it carries.