Osteon: Also called Haversian system, the osteon is the primary organizing unit of skeletal bone. It is the outer portion of the inner canals of the bone, shaped like a long, narrow cylinder that is about 2mm wide and 10mm long. These cylinders are generally parallel to the long axis of the bone but sometime meander a bit. The bones of mammals, birds, and reptiles all contain these cylinders.
In the center of the osteon is a hollow canal, known as the Haversian canal, through which runs blood vessels, nerve fibers, and bone cells called bone lining cells, which are actually osteoblasts. This central canal is surrounded by layers of collagen matrix called lamellae, which are laid down one after the other, each new one inside the older one. These collagen fibers run in a helix or spiral which curves around the central axis. Furthermore, each successive layer runs in a different direction to the layers it is between. This arrangement gives bones strength.
At right angles to the Haversian canals are other canals called Volkmman's (perforating) canals. These canals carry blood vessels through from the periosteum.
Structure of bone showing osteon and Haversian canal.
This page created 30 May 2012 13:17
Last updated 21 Jul 2016 22:17