Facts about bones
Bone: a living dynamic tissue
In the living body, bones are very much alive. They have their own nerves and blood vessels and are made of living cells which help them to grow and to repair themselves. As well, proteins, minerals and vitamins make up the bone.
Babies are born with about 300 soft bones (mostly made of cartilage). During childhood and adolescence, the cartilage grows and is slowly replaced by 'hard' bone. Some of these bones later fuse together, so that the adult skeleton has 206 hard bones.
The major functions of bones are:
- to provide structural support for the body
- to provide protection of vital organs
- to provide an environment for marrow (where blood cells are produced)
- to act as a storage area for minerals (such as calcium)
Bones are made of two types of tissue:
- Hard outer layer called cortical (compact) bone, which is very strong, dense and tough.
- Spongy inner layer called trabecular (cancellous) bone, which is lighter and less dense than compact bone but still very strong.
 Photo by Paul Crompton ©University of Wales College of Medicine |
What is peak bone mass?
By around the age of twenty or twenty-five, the growth process of bones is completed and a person's 'peak bone mass' is normally reached. Peak bone mass is the maximum bone mass achieved in life. The age at which peak bone mass is achieved varies between different parts of the skeleton and different populations. A person's peak bone mass is determined largely by genetic factors, but other factors such as nutrition, physical activity and disease also influence bone development. In youth, optimising peak bone mass as much as possible is important in reducing the risk of osteoporosis later in life.
As we get older we are no longer able to replace bone tissue as quickly as we lose it – in a process called 'bone remodeling'. In women the rate of bone tissue loss increases significantly after menopause, when estrogen production stops and bones no longer benefit from its protective effect. Men also suffer from loss of bone tissue, but the rate of loss is much slower than in women. Lifestyle factors (see prevention) can play a role in helping to reduce age-related bone loss that contributes to osteoporosis risk.
