Osteon

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Osteon


Transverse section of body of human fibula, decalcified. X 250.
Gray's	subject #18 89
Dorlands/Elsevier	o_08/12601039

Osteons (also called Haversian system in honor of Clopton Havers) are predominant structures found in some lamellar or compact bone. Osteons are found in many of the bones of many mammals, birds, reptiles, and amphibians running in a meandering way but generally parallel to the long axis of bones. It is this section of compact bone that is called matrix.

In the center of the osteon is a central canal, called the Haversian canal.

The central canal is surrounded by concentric layers of matrix called lamellae. These lamellae are laid down one after the other over time, each successive one inside the preceding one. Collagen fibers in a lamellae run parallel to each other but the orientation of collagen fibers across separate lamellae is oblique. The fiber density is also lower at the border between adjacent lamellae, which accounts for the distinctive appearance of an osteon.

Osteocytes are found between concentric lamellae and connected to each other and the central canal by cytoplasmic processes through the canals called canaliculi. This network permits the exchange of nutrients and metabolic waste.

Osteons are separated from each other by cement lines. Collagen fibers and canaliculi do not cross cement lines.

The space between separate osteons is occupied by interstitial lamellae, which were formed by pre-existing osteons that have since been reabsorbed.

Osteons are connected to each other and the periosteum by oblique channels called Volkmann's canals.

[edit] Use in archaeology and forensics

Osteons carry their history so that given the right conditions they can be used to "read" the sex, age, health history, motor history and apparently something of the diet of an individual's bone. Osteons and their arrangement also vary according to taxon, so that genus and sometimes species can be differentiated using a bone fragment not otherwise identifiable. This is of use in archaeology, paleontology and forensics.