Bone is living tissue mainly made up of a protein called collagen but it also contains minerals and salts.
Inside the bone there are living cells:
- Osteoblasts (cells that help form bone)
- Osteoclasts (cells that help eat away old bone)
- Osteocytes (mature osteoblasts that have ended their bone forming role)
The actual process of bone formation is called ossification.
During ossification, osteoblasts take calcium from the blood and deposit them in the bone, and osteoclasts reabsorb and break down any old bone.
As a foetus, most of the human skeleton is made up of cartilage, a tough, flexible connective tissue. As the foetus grows, osteoblasts and osteoclasts slowly replace cartilage cells for bone cells and the process of ossification begins. By the time we are born our bones have been partly ossified.
Between the diaphysis (shaft) and the epiphysis (head) of the bone there are cartilage plates called epiphyseal plates. These plates expand causing the bone to grow in length. Ossification is fully complete between the ages of 18 and 30. During this period the stresses of physical activity result in the strengthening of bone tissue.
As the skeleton ages calcium is progressively lost from the bones, which happens earlier in women. Loss of calcium and bone mass can lead to a condition called osteoporosis, which increases the risk of fractures.
The following factors influence bone growth:
Nutrition – Calcium rich foods such as dairy, oily fish and green vegetables are essential for bone health. Excessive intake of caffeine, alcohol, and fizzy drinks can compromise bone health as they reduce the absorption of calcium.
Sunlight – The skin can produce vitamin D when exposed to the ultraviolet portion of sunlight. Vitamin D is essential for the absorption of calcium.
Growth hormone – Secreted by the pituitary gland and responsible for general growth and development of all cells in the body.
Weight bearing exercise – Walking, running and resistance training helps to increase the density of bones, reducing the likelihood of osteoporosis.