RT Book, Section A1 Ash, Rick A1 Morton, David A. A1 Scott, Sheryl A. SR Print(0) ID 1141044837 T1 BONE T2 The Big Picture: Histology YR 2017 FD 2017 PB McGraw-Hill Medical PP New York, NY SN 9780071477581 LK accessbiomedicalscience.mhmedical.com/content.aspx?aid=1141044837 RD 2024/03/29 AB Bone is a specialized connective tissue that comprises most of the skeleton, which supports the entire body. Unlike cartilage, bone tissue is extremely hard and inelastic. This allows the long bones to serve as levers on which muscles act to hold the body upright and move it through space. Bones also provide protective sites for housing the central nervous system (the brain and the spinal cord) as well as the hematopoietic tissue, which is responsible for forming blood cells. The extracellular matrix (ECM) of bone is hardened by the deposition of calcium salts. Bone is thus a reservoir of Ca2+, allowing it to play an important role in regulating the Ca2+ concentration in the blood, a vital activity. Bones begin forming early in embryogenesis and continue growing for about 20 years after birth. Although bone is hard, it does not become a static tissue after growth stops. Bone tissue is turned over by a mechanism that maintains the shape and strength of bone even while portions are being removed and replaced every day. Bone fractures are initially repaired by processes that recapitulate those used in early development, and the restored tissue then is returned to the normal adult form by the continuous activity of turnover. Features of the structure, development, and physiology of bone are intertwined, which complicate a simple understanding of this interesting tissue.