Osteon

Fundamental anatomical unit of compact bone OsteonDiagram of compact bone from a transverse section of a long bone's cortex.DetailsIdentifiersLatinOsteonMeSHD006253Anatomical terminology[edit on Wikidata] Diagram of a typical long bone showing both compact (cortical) and cancellous (spongy) bone. Osteons on cross-section of a bone In osteology, the osteon or haversian system (/həˈvɜːr.ʒən/; named for Clopton Havers) is the fundamental functional unit of much compact bone. Osteons are roughly cylindrical structures that are typically between 0.25 mm and 0.35 mm in diameter. Their length is often hard to define, but estimates vary from several millimeters to around 1 centimeter. They are present in many bones of most mammals and some bird, reptile, and amphibian species. Histogenesis The Haversian system forms during the process of endochondral ossification, which starts with a cartilage template that is gradually replaced by bone tissue. Osteoblasts, the bone-forming cells, secrete the organic components of bone matrix [osteoid] and then initiates its mineralization. As osteoblasts become surrounded by the bone matrix, they differentiate into osteocytes, which reside in the la