As you can see above, and feel on your own body, all of our bones are different shapes. They are shaped the way they are for specific reasons; our bodies shape them while we are growing and developing, into the perfect shape required for the function each one of them must perform.

So, we have long bones such as our femur, irregular bones such as our knee-cap (or patella) and we have flat bones such as our shoulder blade (or scapula).

Bone itself is of two types. Cortical bone which is flat and hard, arranged in sheets on the surface of our bones to give a hard outer layer resisting impact forces. Cancellous bone is a softer bone, which forms a honeycomb-like lattice of struts inside our bones called trabeculae. The structure of these trabeculae gives bone great strength against bending forces; we use the same process ourselves to reinforce many everyday structures such as corrugated cardboard

Bone forms in one of two ways: intramembraneous ossification or endochondral ossification. Intramembraneous ossification involves the direct replacement of sheets of soft connective tissue with bone. Undifferentiated cells in the tissue form bone-making cells called osteoblasts that deposit bone matrix around themselves. Intramembraneous bones are found primarily in the skull. In endochondral ossification, the future bones are first formed as full-scale models made from cartilage. These models become infiltrated by blood vessels that bring osteoblasts to the site. The osteoblasts penetrate the cartilage and replace it with bone. In children, some of the cartilage continues to grow so the developing bones increase in length.

The bones in our body exist in a dynamic equilibrium – there is constant remodeling of existing bone. Old bone is eaten up by specially designed cells called osteoclasts, a process complemented by the laying down of new bone by osteoblasts. This keeps the bone healthy, alive and flexible.

In the course of bone growth or repair, e.g., during childhood development or following a fracture or a surgical procedure, woven bone is laid down rapidly. The fibers in woven are aligned at random and, as a result, have low strength. In contrast, lamellar bone has parallel fibers and is significantly stronger. Woven bone is often replaced by lamellar bone as growth continues or as a bone repair progresses.




More specifically, our bones contain certain substances that are vital to our skeleton's healthy growth, function and repair:
Collagen is a protein that gives bones flexibility. If our bones were simply made of minerals such as Calcium, they would be very brittle and powdery like chalk. Collagen also provides bones with resilience, so that when we do repetitive or strenuous activities our bones can cope. Finally, collagen provides our bones with a framework on which minerals can be laid down, most importantly Calcium Phosphate and Hydroxyapatite (see below).

Hydroxyapatite; don't be put off by the complicated formula: (Ca₁₀(PO₄)₆(OH)₂). This simply tells us that this mineral contains Calcium (Ca), Phosphorous (P), Oxygen (O) and Hydrogen (H).
Hydroxyapatite or 'HA' as it is more commonly know is vital to our bones and skeleton because this mineral gives bones their strength. HA is an extremely hard substance and ensures that bone can bear heavy loads - HA gives us weight-bearing capabilities. One other function that HA performs is that it 'glues' together the collagen fibres in our bone providing a strong and stable matrix or framework.

Growth Factors are vital to bone formation, bone repair and bone remodelling (which we will talk about later in this section). Sometimes a process or reaction requires something to 'trigger' it into action or to encourage the process to take place quickly and efficiently. An example of this might be when you add yeast to flour and water to make bread - bread making simply wouldn't work without yeast. In a similar way, growth factors initiate or stimulate bone growth, repair and remodelling. Growth factors are substances found in blood and bone which are vital for the proper function of bone - they are part of the messaging or communication system which tells our bone what to do - grow, change shape, dissolve away or repair. Some examples of growth factors you may hear are bone morphogenetic protein (BMP), transforming growth factor (TGF) and platelet derived growth factor (PDGF).

Specialized cells are the working part of bone. There are 3 types of cells important to know about:


Osteocytes are mature bone cells, and make up 90% of the cells in bone.

Osteoblasts are responsible for the formation of new bone (osteogenesis).

Osteoclasts are responsible for dissolving bone, and releasing its stored minerals (osteolysis).

As previously mentioned, our bone is dynamic living tissue and is continually renewing itself, so the normal state for our bone is a continual balance between old bone being dissolved and new bone being laid down.




Trace elements are essential for the normal growth and development of the human skeleton. Although they represent a very small portion of bones by weight, they play an important role in bone metabolism, remodeling, and repair. Some examples include fluoride, which is found where new bone is forming and increases bone mass, zinc, which regulates the secretion of hormones that influence the rate of bone turnover, and silicon, which is necessary for the normal formation of the collagen matrix in bone.




If you ask your bones to do something that they wouldn't normally do, then they will 'remodel' accordingly. For example if you wore very pointed narrow toed shoes your toes and feet would re-shape themselves over a long time which would make normal walking difficult for you. Another example is that if you were a manual worker, working physically hard all day, then your bones would be thicker and stronger than someone who spends less time with physical activity. This is why it is important for us all to take regular exercise, to stress our skeleton and make strong healthy bones.

There are times when our bones do not repair themselves or remodel effectively. If you have a disease that effects bone physiology, such as osteoporosis, or are on drugs that may affect bone physiology, such as chemotherapy drugs for cancer, then your bones may need additional help to repair themselves.





First, when our bones are damaged, either through disease, accident, or surgery, the site of the damage will bleed and become inflamed, just as you would expect to happen with your skin. This causes a blood clot to form around the injured bone, known as a haematoma.

Next your body receives the message (via growth factors) that repair is required and you need more specialized cells that build bone (osteoblasts); this is called osteoblast or cell differentiation. The osteoblasts then get to work.

However, the osteoblasts need to have a structure on which to lay down the new bone; they need some scaffolding or a framework to work with. This framework is provided by hydroxyapatite (HA). Your bone cannot grow in a space where there is no other bone at all. It can grow across a small gap - 'bone to bone' for example in a minor break or fracture, but where there is a large gap or space then your bone may need help from doctors and science to repair itself (When might your body need help with bone healing?). When this is the case, and help is required to support your body's natural healing mechanisms, you may need the help of a bone graft substitute, or synthetic bone product, such as ApaPore, a hydroxyapatite bone graft substitute.

When your bone has a good framework for bone to be laid onto, and your osteoblasts have lain down new bone cells, you are left with a callous at the site of injury, in the same way as you would expect a scab on your skin when you have cut yourself. The final phase of bone repair is remodelling of this callous back to as close as possible to the bone's original shape. This task is performed by the osteoclasts.



Extensive research on dietary silicon has shown that silicon is a critical factor in normal bone development. The mineral phase of normal bone is hydroxyapatite with varying amounts of trace elements such as silicon and zinc. X-ray analysis has identified silicon in growth areas in the developing bones of young people. In adults, silicon is localized in active osteoblasts (bone forming cells) and is a major ion of bone forming cells (on a par with calcium, phosphorous and magnesium). Silicon is localized in those specific portions of tissues associated with calcification. Its importance in bone formation and repair is well established.