Bones are made up of hard connective tissue, the main constituent of approximately all skeletal systems in adult vertebrate animals. Bone emerges to be nonliving in fact, the word skeleton is derived from a Greek which means dried up. Nevertheless, bone essentially is a dynamic structure composed of both living tissues, such as bone cells, fat cells, and blood vessels, and nonliving materials, including water and minerals. Bones are versatile structures that play different, very important roles in vertebrates. They offer a framework for the body, supporting it and giving it shape. They also provide a surface for the attachment of muscles and act as levers, permitting many complex movements. Numerous bones shield softer internal organs; for instance, skull bones protect the brain, and rib bones form a cage around the lungs and heart. Additionally to these structural and mechanical functions, bones also participate in the body’s physiology. They accumulate calcium, a mineral essential for the activity of nerve and muscle cells. The soft core of bone, the bone marrow, is the site of formation of red blood cells, certain white blood cells, and blood platelets. An adult human has 206 bones, which account for 14 percent of the body’s total weight. The longest and strongest bone is the thighbone, which at maturity is about 50 cm (20 in) long and 2.5 cm (1 in) wide. The smallest bone, the stirrup bone, is one of three tiny bones buried within the middle ear; it is only 0.18 cm (0.07 in) long.( Purves, W.K., Orians, G.H., Heller, H.C., and Sadova, D. (1995))
Bone consists of living cells widely scattered within a nonliving material called the matrix. The matrix is formed by osteoblasts, cells that are constantly renewed in the bone........
