The bones that form our skeleton are the major structural organ that supports our bodies. The hard bone tissue supports the soft tissue of other internal organs; bones provide anchor points for most skeletal muscles and thus enable movement. In addition, bones protect the internal organs from injury (for example, the brain is protected by the skull), bones act as storage of minerals (and help the body balance its mineral metabolism) and the bone marrow plays an essential role in the production of red blood cells.
In line with the multiple tasks of bones in our bodies, bones consist of various different tissues: compact (cortical) and spongy (cancellous) bone tissue, as well as bone marrow, nerves, small blood vessels and epithelium (lining tissue) and a dense layer of connective tissue enveloping bones (periosteum). The compact, cortical bone tissue forms the outer layer of all bones; it is a dense and strong material.
Bones continually renew themselves, similar to the ongoing renewal of skin. There are two types of bone cells involved in this renewal process: osteoclasts break down bone tissue, and osteoblasts build new bone tissue. Osteoblasts form the mineralised connective tissue that we usually call bone; the mineralised material is a slightly disordered crystalline phosphate mineral, called hydroxyapatite.
Like any other organ in the body, bones also develop diseases and lesions. Excluding fractures (broken bones) here (discussed separately), bone lesions can be broadly divided into three groups:
- inflammatory (including bone infections) and other non-neoplastic lesions
- benign neoplastic lesions (benign lumps)
- malignant neoplastic lesions (bone cancers).
Primary malignant bone lesions are rare. Inflammatory bone lesions cover a fair range of conditions, as do benign neoplastic bone lesions – and nearly all of these non-malignant bone conditions have considerable overlap with other systemic or local conditions (ranging from jaw cysts to rheumatoid arthritis, and everything in between).
Next section: Bone lesion