A connective tissue which is impregnated with large deposits of calcium salts, mainly calcium phosphate. The salts make the bone extremely hard. Bone is formed by the process of ossification which is the formation of bone tissue from cartilage or membrane. This involves the laying down of bone by bone cells or osteoblasts. The osteoblasts arrange themselves in rings around nerves and blood vessels. Eventually the osteoblasts surround themselves with bone and at this stage they are called osteocytes. This type of bone is called compact Haversian bone. Spongy bone is less compact and not as hard as compact bone. Compact bone is found in the shafts of the limb bones, while spongy bone is found at the ends of these bones. Covering the bone is a dense layer of connective tissue called the periosteum.
Bones have a variety of functions including:
• movement and stability – bones form a supporting body framework and provide attachments for muscles, ligaments and tendons which reinforce the support and movement of the body
• protection – bones form a framework which protects the organs of the body
• storage – bones store minerals such as calcium, phosphorus and magnesium
• cell production – red blood cells are manufactured in the bone marrow.
The structure of a long bone