:For other uses of the word "bone", see bone (disambiguation).thumb Gray's illustration of a human femur, a typically recognized bone.
Bone refers either to a hardened connective tissue or to one of the individual structures, or organs, into which it is formed, found in many animals. Bones support body structures, protect internal organs, and (in conjunction with muscles) facilitate movement; are also involved with cell formation, calcium metabolism, and mineral storage. The bones of an animal are, collectively, known as the skeleton.
Evolutionary alternatives, to bones, are shells and chitin.
1 General overview
It is a relatively hardThe Rockwell scale characterises the indentation hardness of materials through the depth of penetration of an indenter, loaded on a material sample and compared to the penetration in some reference material. It is one of several definitions of hardness in and light- weightFor the 1994 album by the group Rollins Band, see Weight (album). Weight is the force exerted upon an object by virtue of its position in a gravitational field. In a constant gravitational field, such as the Earth's, this force is proportional to the obje composite materialComposite materials (or composites for short) are engineering materials made from two or more components. One component is often a strong fibre such as fiberglass, kevlar or carbon fibre that gives the material its tensile strength, while another componen, formed mostly of calcium phosphate (in the chemical arrangement termed calcium hydroxyapatite), which has relatively high compressive strengthCompressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength. Compare tensile strength. though poor tensile strength. While bone is essentially brittle, it does have a degree of significant elasticityThere are separate articles about elasticity in economics, and about British rubber bands. In solid mechanics, the adjective elastic characterises both collisions between, and deformations of, physical objects. A collision is perfectly elastic if the tota contributed by its organic components (chiefly collagenCollagen is the main protein of connective tissue. It has great tensile strength, and is the main component of ligaments and tendons. It is responsible for skin elasticity, and its degradation leads to wrinkles that accompany aging. Collagen also fills ou). Bone is a meshA mesh is similar to fabric or a web in that it has many connected or weaved pieces. In clothing, a mesh is often defined as fabric that has a large number of closely-spaced holes, such as is common practice for modern sports jerseys. Meshes are often use, the densityFor other meanings of density, see density (disambiguation Density (symbol: rho Greek: rho) is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass div of which may vary at different points.
2 Forms of bone
Bone can be either cortical ("compact") or cancellous ("spongy"). Cortical bone makes up a large portion of skeletal mass; but, because of its density, it has a low surface area. Cancellous bone is trabecular, it has a relatively high surface area, but forms a smaller portion of the skeleton.
Bone can also be either woven or lamellar. Woven bone is put down rapidly during growth or repair. It is so called because its fibres are aligned at random, and as a result has low strength. In contrast lamellar bone has parallel fibres and is much stronger. Woven bone is often replaced by lamellar bone as growth continues.
"Long bones" are tubular in structure, and the hollow middle is filled with yellow marrow. While the majority of long bones are formed of cortical material; at the ends are the epiphysis, which are generally composed of cancellous material and red marrow.
