Osteoporosis - Introduction

Introduction

Osteoporosis is a skeletal disease in which bones become brittle and prone to fracture. In other words, the bone loses density. Bone density is the amount of bone tissue (such as calcium and minerals) in a certain volume of bone. Osteoporosis is diagnosed when bone density has decreased to the point where the risk of fractures is high even without severe stress or injury to the bones.

The Bones

The Function of Bones. The skeleton has a dual function:

• It provides structural support for muscles and organs.
• It also serves as a storehouse for the body's calcium and other essential minerals, such as phosphorus and magnesium.

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The skeleton holds 99% of the body's calcium. The remaining 1% circulates in the blood and is essential for crucial bodily functions, ranging from muscle contraction to nerve function to blood clotting.

Bone Turnover: the Breakdown and Rebuilding of Bones. Bone tissue is constantly being broken down and reformed again. This turnover is necessary for growth, for repair of minor damage that occurs from everyday stress, and for the maintenance of a properly functioning body. Two essential cells are involved in this process:

• Osteoclast cells are formed from certain blood cells and are responsible for the breakdown, or resorption, of the skeleton. These cells dig holes into the bone and release the small amounts of calcium into the bloodstream that are necessary for other vital functions.
• Osteoblast cells are produced by bone cells and are the bone builders. They rebuild the skeleton, first by filling in the holes with collagen, and then by laying down crystals of calcium and phosphorus.

Each year, about 10 - 30% of the adult skeleton is remodeled in this way. The balance of bone build-up (formation) and break down (resorption) is controlled by a complex mix of hormones and chemical factors. If bone resorption occurs at a greater rate than bone build up, your bone loses density and puts you at risk for osteoporosis.