Bone tissue

Bone tissue
Cross-section of a long bone showing both spongy and compact osseous tissue
Identifiers
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terminology [[[d:|edit on Wikidata]]]

Bone tissue, or osseous tissue, is the major structural and supportive connective tissue of the body. Bone tissue forms the rigid part of the bones that make up the skeleton.

Bone tissue is different from bones themselves — bones are organs made up of bone tissue as well as marrow, blood vessels, epithelium and nerves, while bone tissue refers specifically to the bone mineral matrix that forms the rigid sections of the organ, and the bone cells within it.

Structure

There are two types of bone tissue: cortical bone and cancellous bone. Cortical bone is synonymous with compact bone, and cancellous bone is synonymous with trabecular and spongy bone. Cortical bone forms the extremely hard exterior while cancellous bone fills the hollow interior. The tissues are biologically identical; the difference is in how the microstructure is arranged.

Formation

Bone tissue is a mineralized connective tissue. It is formed by cells, called osteoblasts, that deposit a matrix of Type-I collagen and also release calcium, magnesium, and phosphate ions that ultimately combine chemically within the collagenous matrix into a crystalline mineral, known as bone mineral, in the form of carbonated hydroxyapatite. The combination of hard mineral and flexible collagen makes bone harder and stronger than cartilage without being brittle. Cortical bone consists of a repeating structure called an osteon or Haversian system, which is the primary anatomical and functional unit. Each osteon has concentric lamellae (layers) of mineralized matrix, which are deposited around a central canal, known as the Haversian canal, each containing a blood and nerve supply.

Compact bone (cross-section). (Haversian system and osteocytes).

Osteoblasts. actively synthesizing osteoid with two osteocytes.

Osteoclast with multiple nuclei and a "foamy" cytosol.

Function

Bone tissue performs numerous functions including:

Directly:

• Support for muscles, organs, and soft tissues.
• Leverage and movement.
• Protection of vital organs, e.g., the heart. (Note: not all vital organs are protected by bones, e.g., the intestines.)
• Calcium phosphate storage.

Indirectly:

• Hemopoiesis - formation of blood cells by the bone marrow interspersed within the spongy bone.

See also

• Periosteum
• Bone healing
• Osseointegration
• Osteocyte
• Osteoclast

Sources

• Henry Gray: Anatomy of the human body (Bartleby.com; Great Books Online)
• Eldra P. Solomon - Richard R. Schmidt - Peter J. Adragna : Human anatomy & physiology ed. 2nd 1990 (Sunders College Publishing, Philadelphia) ISBN 0-03-011914-6