Physiology — bone processes, functions and fracture

At the Center for Better Bones, we believe that the state of health is the norm in the natural world, rather than the exception. In the functional medicine model, allostasis, or “dynamic stability through change” is regarded as the default condition. In observing all the creatures in the animal kingdom around us, we can see that lifelong bone health is a birthright with which Mother Nature has blessed us, for we too, are given ample bone to last our whole lives through.

This leads us to wonder what physiological conditions are causing bone health to deteriorate long before the ends of so many people’s lives today. What robs our bones of their innate capacity to repair themselves so that fracture can be avoided?

To answer this question, we can look first to the physiology of bone, and then to the physics

You may recall from high school science class that physiology is all about function. But there is much more to physiology than function alone. More formally, the American Heritage Scientific Dictionary defines physiology as:

The scientific study of an organism’s vital functions, including:

  • growth and development
  • the absorption and processing of nutrients
  • the synthesis and distribution of proteins and other organic molecules
  • the functioning of… tissues, organs, and other anatomic structures

If the skeleton is the organ under consideration here, and our bones the tissues, the physiology of bones can be defined as the study of their “normal mechanical, physical, and biochemical processes.”

As explained in the above section on risks for fracture, bone mineral density (BMD) is an obvious and important determinant. From the physiological standpoint, however — the aspect that involves the growth and development of bone with respect to its function — the demineralization of bone is the metabolic process most integral to tipping bone toward health or disease. A high rate of bone protein matrix breakdown — that is, a high bone resorption rate — will leave bones bereft of collagen. Collagen is the living elastic tissue that imparts flexibility and resilience to bone, the qualities necessary to withstand the stress and strain they encounter as we go about our everyday lives. Slowing the demineralization process becomes particularly critical for skeletal health with advancing years.

At the cellular level, bone demineralization is the result of a complex interplay of messenger molecules, key nutrient availability, enzymes, cleavers, and countless other physiological variables. Bone can be visualized as a living protein sponge matrix upon which mineral crystals are embedded. As we lose bone, this living protein matrix is broken down by osteoclasts and excreted from our bodies in our urine. The amount of bone protein fragments found in the urine is a direct reflection of rate of bone resorption taking place in our bodies. A number of urine tests are available that detect these urinary indices of skeletal turnover. They are as useful, and in some cases more useful, than bone density tests in evaluating the rate of bone breakdown, and offer an alternative tool for predicting fractures, independent of bone density. Indeed, the combination of high rate of bone resorption together with low bone density is particularly predictive of fracture risk.

Now, this is just the short version — there is much more about the biochemical processes that build bone and then break it down in an ongoing, give-and-take process that never ceases until the day we die.

Please click here for information on the physics — what physical conditions in the bones predispose them to fracture?.

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