is a rigid organ that forms part of the endoskeleton of vertebrates.
Bones function to:
• move, support, and protect the body,
• produce red and white blood cells,
• store minerals.
Bones have a complex internal and external structure, allowing them to be
lightweight yet strong and hard, while fulfilling their many other functions.
Bone tissue, or mineralised osseous tissue, gives bones their rigidity and
honeycomb-like three-dimensional internal structure.
Other tissue types found in bones include marrow, the periosteum, nerves,
blood vessels and cartilage.
The primary tissue of bone, osseous tissue, is a relatively hard and
composite material, formed mostly of calcium phosphate in the chemical
arrangement termed calcium hydroxylapatite (this is the osseous tissue that
gives bones their rigidity).
It has relatively high compressive strength but poor tensile strength,
resists pushing forces well, but not pulling forces.
While bone is essentially brittle, it does have a significant degree of
contributed chiefly by collagen.
All bones consist of living cells embedded in the mineralised organic
makes up the osseous tissue.
Bone is not a uniformly solid material:
• The hard outer layer of bones is called compact bone tissue due to its
minimal gaps or spaces. Also known as dense or cortical bone.
• This tissue gives bones their smooth, white, solid appearance, and accounts
for 80% of the total bone mass of an adult skeleton.
• Filling the interior is the hole-filled spongy bone tissue (also called
or trabecular bone) 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 (except where they interact with other bones through
joints) is 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.