Bone Basics

Peer Reviewed

The human skeleton is composed of 206 bones, 33 of which are located in the spine. Bones are long, flat, short or irregularly shaped, and some are thicker than others. Bones are flexible during youth, eventually becoming rigid at maturity. If a bone is broken, collagen, which is manufactured by the body, mends the fracture. The new bone is then hardened through a process termed calcification.

Bone is a living organ comparable to the heart or kidneys. It contains blood vessels and is nourished through circulation. If any bone or organ system is ignored or misused, it can decay and cause problems. Within bone are two compartments. The outer layer is termed cortical bone and the inner is cancellous bone. Microscopically, cortical bone looks like concentric rings. Cancellous bone resembles latticework and is spongy. A system of blood vessels supplies the bones with needed nutrition.

Bones serve as storehouses for minerals and fats. Approximately a quarter of a bone's weight is fluid. Minerals make up the remaining weight along with other nutrients.

The semi soft center of the bone contains marrow. Marrow is similar to a busy factory manufacturing red blood cells, which are necessary to adequately distribute oxygen throughout the body. In fact, each time the heart beats approximately 10% of the blood is pumped into the skeletal system!

Throughout a person's lifetime, bone continuously breaks down and rebuilds itself. Sometime after the age of 50, bone naturally begins to lose strength. This loss may progress due to decreased demands placed on the skeletal system.

This article is an excerpt from the book Save Your Aching Back and Neck: A Patient’s Guide, edited by Dr. Stewart Eidelson.

Updated on: 02/15/10
Mark R. McLaughlin, MD
Dr. Eidelson's article describes the structure of the spine's bones. His book "Save Your Aching Back" is an outstanding contribution to the lay public's literature regarding spinal disorders. I have used his material often when I educate my patients in the office. He is to be commended for his lifelong dedication to patient education.