The skeleton is made up of bone that is remodelled on a regular basis – new bone tissue is built, while old bone tissue is broken down. Bones and joints respond to physical exercise and diet. Weight-bearing exercise helps to build and maintain bone strength, especially as we age, while a nutritious diet means that your body has enough calcium and vitamin D to build and maintain a healthy skeleton.
Three cell types in the bones control the renewal process:
- osteoblasts – form or build new bone tissue and repair old bone
- osteocytes – are inactive osteoblasts that communicate with osteoblasts and osteoclasts
- osteoclasts – break down or destroy old bone by releasing enzymes and acids to dissolve minerals and digest old bone (resorption) and remodel damaged bones.
Bone and joint diseases and disorders
The complex function of bones means that they are susceptible to a range of diseases and disorders including:
- osteoporosis – weak and brittle bones are caused by loss of bone density and mass
- osteoarthritis – a degenerative joint disease where cartilage between bones is damaged
- rheumatoid arthritis – an autoimmune disease causing joint pain and inflammation
- bone cancers – a cancer that starts in cells found in your bones such as osteosarcoma
- blood cancers – a cancer that starts in bone marrow, which is where new blood cells are made and stored (e.g. leukemia)
- brittle bone disease – an inherited genetic condition that results in bones that are very fragile and fracture or break easily (osteogenesis imperfecta).
Understanding the interactions of cells in bone helps drive research to discover and develop treatments for bone-related diseases and musculoskeletal conditions. Regenerative strategies to repair bone and tissue are under investigation, as are the use of biomaterials and 3D printing for orthopaedic implants.
Implantable bionic devices are being used to dampen the immune response and prevent long-term damage to the joint in arthritis. Researchers are also examining the relationships among cells in the bone and the immune system, in a field known as osteoimmunology.
Image caption: Human cartilage – hyaline and elastic.
Image credit: Stockvault