Human Anatomy

Bones

The primary tissue of bone, osseous tissue, is a hard and lightweight composite material, formed mostly of calcium phosphate in the chemical arrangement termed calcium hydroxylapatite. It has high compressive strength but poor tensile strength, meaning it resists pushing forces well, but not pulling forces. While bone is essentially brittle, it does have a significant degree of elasticity contributed chiefly by collagen. All bones consist of living cells embedded in the mineralised organic matrix that makes up the osseous tissue.

Bone is not a uniformly solid material, but rather has some spaces between its hard components. The hard outer layer of bones is called compact bone tissue. This tissue gives bones their smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult skeleton. Filling the interior of the organ is the hole-filled spongy bone tissue which is comprised of a network of flat or needle-shaped trabeculae which makes the overall organ lighter and allows room for blood vessels and marrow.

Spongy bone accounts for the remaining 20% of total bone mass, but has nearly ten times the surface area of compact bone. The exterior of bones are covered by the periosteum, which has an external fibrous layer, and an internal osteogenic layer. The periosteum is richly supplied with blood, lymph and nerve vessels, attaching to the bone itself through Sharpey's fibres.

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