Chapter 6. Bone

A. Introduction

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Bone is a connective tissue specialized to offer a greater degree of support and protection to soft tissues than is provided by cartilage. It is the principle tissue of the adult skeletal system, offering the primary support and protection needed by the body's soft tissues, and it serves as an important dynamic calcium reservoir that participates in the regulation of blood calcium concentration.

Bone tissue is significantly harder than cartilage, allowing bone to bear significantly more weight at the expense of flexibilty. The extracellular fibers of the matrix are largely collagen type I fibers, and the organic component of its ground substance is extemely similar to that of cartilage. Its enhanced protective and supportive characteristics are achieved through mineralization of the extracellular matrix, which results in a an extremely hard, relatively inflexible tissue. The mineral is primarily calcium and phosphate, deposited in the form of hydroxyapatite crystals on the collagen fibers. The hardness of bone tissue prevents it from growing internally. Therefore, the growth of many bones depends on the presence of cartilage.

As a tissue, bone has two principle functions. It is the principle tissue of the adult skeletal system, offering the primary support and protection needed by the body's soft tissues, and it serves as an important dynamic calcium reservoir that participates in the regulation of blood calcium concentration.