Essentials of Bone Densitometry for the Medical Physicist

Human Skeleton: The human skeleton consists of over 200 bones of different sizes and shapes that play a variety of roles in maintaining our health and well-being. Bones provide the basic structural framework for our muscles and allow us to stand upright and move about. Bones also encase and protect sensitive organs of the body such as the brain, heart, spinal cord and eyes from injury from external forces. Teeth are hard specialized bones which provide us nourishment by grinding and tearing our food. The tiniest bones of the body are those that reside in the inner ear which provide a transmission path for sound vibration to reach the brain and enables us to hear. Bones also play a hidden but equally important role in the biochemistry of our bodies serving as a reservoir for calcium which is essential for the proper nerve conduction and muscle action. Because of calcium’s importance, its level in the blood is closely monitored and regulated; if it falls too low, calcium is released from the bone to maintain the proper level in the blood and excreted if the calcium level is too high. Maintaining the proper level is termed homeostasis and involves complex regulatory mechanism beyond the scope of this discussion.