Bone

This article is about the skeletal organs. For the tissue, see Osseous tissue. For other uses, see Bone (disambiguation).

Drawing of a human femur.

Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue. Because bones come in a variety of shapes and have a complex internal and external structure they are lightweight, yet strong and hard, in addition to fulfilling their many other functions. One of the types of tissue that makes up bone is the mineralized osseous tissue, also called bone tissue, that gives it rigidity and a honeycomb-like three-dimensional internal structure. Other types of tissue found in bones include marrow, endosteum and periosteum, nerves, blood vessels and cartilage. There are 206 bones in the adult human body^[1] and about 270 in an infant.^[2]

[edit] Functions

Bones have nine main functions:

Mechanical

• Protection — Bones can serve to protect internal organs, such as the skull protecting the brain or the ribs protecting the heart and lungs.
• Shape — Bones provide a frame to keep the body supported.
• Movement — Bones, skeletal muscles, tendons, ligaments and joints function together to generate and transfer forces so that individual body parts or the whole body can be manipulated in three-dimensional space. The interaction between bone and muscle is studied in biomechanics.
• Sound transduction — Bones are important in the mechanical aspect of hearing.

Synthetic

• Blood production — The marrow, located within the medullary cavity of long bones and interstices of cancellous bone, produces blood cells in a process called haematopoiesis.

Metabolic

• Mineral storage — Bones act as reserves of minerals important for the body, most notably calcium and phosphorus.
• Fat Storage — The yellow bone marrow acts as a storage reserve of fatty acids
• Acid-base balance — Bone buffers the blood against excessive pH changes by absorbing or releasing alkaline salts.
• Detoxification — Bone tissues can also store heavy metals and other foreign elements, removing them from the blood and reducing their effects on other tissues. These can later be gradually released for excretion.^{[citation needed]}Also they contain yellow bone marrow.

[edit] Characteristics

The primary tissue of bone, osseous tissue, is a relatively hard and lightweight 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 of 104-121 MPa, 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 mineralized organic matrix that makes up the osseous tissue.

[edit] Masto-structure

[edit] Gross anatomy

See also: Human skeleton and List of bones of the human skeleton