Age Related Changes to Bone
The major age related change in the skeletal system is the loss of calcium in the bone. As previously discussed calcium homeostasis is critical to maintaining bone structure. As one ages this homeostasis is disrupted, which results in a weakening of the bones. While the exact causes of the disruption are not fully understood it has been observed that bone loss is more severe in women that men. In women bones begin to lose calcium around the age of 30. By the age of 70 women may have lose 30% or more of their bone calcium. Most men don’t begin to the lose calcium until they reach the age of 60.
In addition to the lose of calcium as one ages protein synthesis also slows. As a result there is little to no new formation of collagen fibers. These fibers are what give the bones strength and flexibility. Without them bones become brittle resulting in a higher rate of fracture.
Finally bone reabsorption continues without the continued formation of new bone. This results in larger centrally located medullary cavities of the long bones and thinner walls of compact bone.
All of these changes result in a decrease of bone mass. While the causes of these changes are not well understood, it is thought that hormonal imbalances and changes in activity level may be factors.
Age Related Changes to Cartilage
One of the main roles of the skeletal system is the smooth functioning of the various movable joints of the body. Articular cartilage covers the ends of bone involved in a joint. As the joint moves articular cartilage rubs against articular cartilage, as opposed to bone on bone contact. This cartilage reduces friction and produces smooth movements in the joints. As you age this cartilage becomes thinner and deteriorates. The resulting bone on bone contact makes movement of the joint painful.
Costal cartilage has the specific function of connecting the ribs to the sternum. This cartilage make it possible for the rib cage to expand and contract with respiration. As one ages the cartilage calcifies resulting in a loss of flexibility. This restricts breathing.
Fibrocartilage makes up the intervertebral discs which specifically provides cushioning between the vertebrae which make up the spinal column. After the age of about 40 years of age, the cartilage experiences a gradual loss of cells and water. This results in a decreased level of cushioning provided by these discs.