Bones begin life as cartilage. As a baby develops in their mother's womb, the skeletal system becomes organised into a framework of cartilage. Before birth, there is a certain amount of hardening of the limb bones to allow some mammals to stand shortly after delivery. However, the greater part of the skeleton is cartilaginous at birth. After birth, the skeleton starts to harden as calcium and other minerals are deposited in the bone tissue. This process continues throughout life until, in old age, very little cartilage is left and the bones are old and brittle. The process of hardening cartilage into bone is called ossification.

Ossification is achieved by bone-forming cells called osteoblasts (osteo- means "bone" in Greek). The old osteoblasts produce bone tissue, which is also called osteotissue, and also secrete the enzyme phosphatase which allows calcium salts to be deposited in the newly formed bone tissue. This makes the tissue hard or bone-like.

The osteoblasts are connected by a system of tiny canals called canaliculi which bring tissue fluid to each osteoblast. The canals and special cells make a network which forms the frame of the bone. The newly made bone tissue is laid down on this mould and becomes calcified or hardened over time.

Once the bone tissue is hardened and mature, the osteoblasts change into osteocyctes (mature bone cells). The osteocytes sit in small cavities called lacunae within the calcified or hardened bone tissue. The system of canals still connects the lacunae and now serves to carry tissue fluid that is essential for the maintenance of life of the osteocytes.

Who Needs to Understand Bones?

A knowledge of how bones are made and work is important for anyone working in allied health industries. Fitness and sporting professionals need to understand the interactions between bones and muscles to properly understand and manage human movement. Nutritionists need to understand bones to properly manage diet. Biology teachers teach people about bones; physiotherapists help people rehabilitate after injuries, and first aid officers need to understand the bone structure so they can help and not hinder in an emergency.

So many people spend much of their lives sitting or focused on a computer screen. This means that the potential for chronic bone and muscle problems has greatly increased. An understanding of bones and muscles can help you better manage yourself and those around you. A detailed understanding of bones can also support the career prospects of those involved in health, safety or fitness professions.

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