Skeletal Bones

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The human skeleton is composed of 206 bones, of which 33 are located in the spine. Bones come in all shapes and sizes, and are flexible during youth, eventually becoming rigid at maturity. Contrary to what many people may think, bone is a living organ comparable to the heart or kidneys. It contains blood vessels and is nourished through circulation like other tissues of the body. If a bone is broken, the fracture is mended by a substance produced by your body called collagen. The new bone is then hardened through a process termed calcification.

Bones contain two layers, the outer cortical bone and the inner cancellous bone. Microscopically, cortical bone looks like concentric rings, whereas cancellous bone appears spongy. A system of blood vessels supplies the bones with needed nutrition. Bones store minerals and fats, and approximately 25% of a bone's weight is fluid. Minerals make up the remaining weight along with other nutrients.

The center of the bone contains marrow, a semi-soft substance. Marrow is involved in manufacturing red blood cells, which are necessary to distribute oxygen throughout the body. Throughout a person's lifetime, bone continuously breaks down and rebuilds itself, however, sometime after the age of 50, bone naturally begins to lose strength as less demands are placed on the skeletal system.