Osteon

Osteon or Haversian system is the fundamental functional unit of much compact bone. Osteons are cylindrical structures that contain a mineral matrix and living osteocytes connected by canaliculi, which transport blood. They are aligned parallel to the long axis of the bone. Each osteon consists of concentric layers, or lamellae, of compact bone tissue that surround a central canal, the Haversian canal.

Structure

The Haversian canal (HC) is the central canal within the osteon. It contains the bone's blood vessels and nerve fibers. Surrounding the HC are concentric layers (lamellae) of bone matrix, which makes up the bulk of the osteon. Between the lamellae are small spaces called lacunae. These lacunae contain osteocytes, the cells that maintain the bone. Tiny canals called canaliculi connect the osteocytes with each other and the HC.

Function

Osteons are the structural unit of compact bone. Each osteon individually is made up of concentric layers of collagen and calcified matrix, which are arranged around a central Haversian canal. The Haversian canal contains the bone's blood supply. The arrangement of osteons allows for efficient nutrition and waste removal.

Clinical significance

Changes in the structure and function of the osteons can lead to bone diseases. For example, osteoporosis is a condition that weakens bones and makes them more prone to fracture. This occurs when the creation of new bone doesn't keep up with the removal of old bone. Osteoporosis affects the entire skeleton, but has its most serious consequences when it leads to hip and vertebral fractures.

See also

• Bone tissue
• Compact bone
• Haversian canal
• Osteoporosis

References

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  Transverse section of bone

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  Illustration of compact and spongy bone

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  Bone connective tissue

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  Compact bone histology