When people think of their bones, they often think of them as lifeless structures. This, however, is not the case. Bone is living tissue that is in a constant state of regeneration, much like the kidneys, heart, and other organs of the body.
Bone consists of two important components: collagen and mineral. Bone is mostly made up of collagen. Collagen provides a soft framework and gives bones necessary flexibility. The mineral component includes calcium and phosphate and hardens the collagen framework. Bones must maintain a balance of collagen and mineral so that they are strong, yet flexible enough, to withstand stress.
We reach our peak bone mass around the age of 30. However, our bones are changing constantly throughout our lives. This process is known as "remodeling" and there are two important types of bone cells to be familiar with: osteoclasts and osteoblasts. Osteoclasts are responsible for removing old or worn bone, which can leave cavities (lacunas). The removal of bone, and the creation of lacunas, is known as bone resorption. It is the job of the osteoblasts to fill these lacunas with new collagen and mineral, a process known as bone formation.
Just as healthy bone structure requires adequate amounts of collagen and mineral, there must also be a healthy balance of bone resorption and formation. If the amount of new bone deposited by osteoblasts equals the amount of bone taken away by osteoclasts, the bones stay strong. However, after we reach our peak bone mass, the balance tends to shift, with more bone being taken away than deposited.