Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine (TGF-β, IGF) signalling.

Ossification (or osteogenesis) is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of normal, healthy bone tissue:[1] Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme), while endochondral ossification involves cartilage as a precursor. In fracture healing, endochondral osteogenesis is the most commonly occurring process, for example in fractures of long bones treated by plaster of Paris, whereas fractures treated by open reduction and stabilization by metal plate and screws may heal by intramembranous osteogenesis.

Heterotopic ossification is a process resulting in the formation of bone tissue that is often atypical, at an extraskeletal location. Calcification is often confused with ossification. Calcification is synonymous with the formation of calcium-based salts and crystals within cells and tissue. It is a process that occurs during ossification, but not vice versa.

The exact mechanisms by which bone development is triggered remains unclear, but it involves growth factors and cytokines in some way.


Timetable for human ossification

Time period[2] Bones affected[2]
Third month of embryonic development Ossification in long bones beginning
Fourth month Most primary ossification centers have appeared in the diaphyses of bone.
Birth to 5 years Secondary ossification centers appear in the epiphyses
5 years to 12 years in females, 5 to 14 years in males Ossification is spreading rapidly from the ossifcation centers and various bones are becoming ossified
17 to 20 years Bone of upper limbs and scapulae becoming completely ossified
18 to 23 years Bone of the lower limbs and os coxae become completely ossified
23 to 25 years Bone of the sternum, clavicles, and vertebrae become completely ossified
By 25 years Nearly all bones are completely ossified


Several hypotheses have been proposed for how bone evolved as a structural element in vertebrates. One hypothesis is that bone developed from tissues that evolved to store minerals. Specifically, calcium-based minerals were stored in cartilage and bone was an exaptation development from this calcified cartilage.[3] However, other possibilities include bony tissue evolving as an osmotic barrier, or as a protective structure.

See also


  1. ^ Caetano-Lopes J, Canhão H, Fonseca JE (2007). "Osteoblasts and bone formation". Acta reumatológica portuguesa 32 (2): 103–10. PMID 17572649. 
  2. ^ a b Predicting Height from the Length of Limb Bones Part of: Examining Effects of Space Flight on the Skeletal System. Emily Morey-Holton. NASA Ames Research Center. Moffett Field, California
  3. ^ Donoghue PC, Sansom IJ (2002). "Origin and early evolution of vertebrate skeletonization". Microsc. Res. Tech. 59 (5): 352–72. doi:10.1002/jemt.10217. PMID 12430166. 

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Look at other dictionaries:

  • ossification — [ ɔsifikasjɔ̃ ] n. f. • 1697; de ossifier 1 ♦ Formation du tissu osseux par transformation d un tissu fibreux ou cartilagineux en substance osseuse. ⇒ ostéogenèse. Point, centre d ossification. Ossification des fontanelles. 2 ♦ Production… …   Encyclopédie Universelle

  • Ossification — Os si*fi*ca tion, n. [Cf. F. ossification. See {Ossify}.] 1. (Physiol.) The formation of bone; the process, in the growth of an animal, by which inorganic material (mainly lime salts) is deposited in cartilage or membrane, forming bony tissue;… …   The Collaborative International Dictionary of English

  • Ossification — (v. lat.), 1) Knochenbildung (s.d.); 2) Verknöcherung. Ossificationspunkte (Puncta ossificationis), die in einem nicht bleibenden Knorpel zuerst sich knöchern zeigenden Stellen, von denen die weitere Knochenbildung anhebt …   Pierer's Universal-Lexikon

  • Ossification — Ossification, lat. deutsch, Knochenbildung, Verknöcherung …   Herders Conversations-Lexikon

  • ossification — 1690s, from L. ossis (gen. of os) of bones (see OSSEOUS (Cf. osseous)) …   Etymology dictionary

  • Ossification — Ostéogenèse L ostéogenèse est le processus par lequel s élabore le tissu osseux. L os est formé à partir : d une matrice organique (35%) composée essentiellement de collagène de type I (90%), mais aussi d autres protéines comme l… …   Wikipédia en Français

  • ossification — (o ssi fi ka sion) s. f. 1°   Terme d anatomie. Génération des os, développement normal du système osseux. •   À deux mois, le foetus a plus de deux pouces de longueur ; l ossification est sensible au milieu du bras, de l avant bras, de la cuisse …   Dictionnaire de la Langue Française d'Émile Littré

  • Ossification — The process of creating bone, that is of transforming cartilage (or fibrous tissue) into bone. The human skeleton initially consists largely of cartilage which is relatively soft and is gradually transformed into hard bone during infant and child …   Medical dictionary

  • OSSIFICATION — s. f. Formation des os, changement insensible des parties membraneuses et cartilagineuses en os. L ossification se fait peu à peu. L ossification du coeur, de l aorte. Le point d ossification …   Dictionnaire de l'Academie Francaise, 7eme edition (1835)

  • OSSIFICATION — n. f. Formation des os. Cet anatomiste a étudié l’ossification dans le foetus. Il se dit aussi du Changement insensible des parties membraneuses et cartilagineuses en tissu osseux. L’ossification du coeur, de l’aorte. Le point d’ossification …   Dictionnaire de l'Academie Francaise, 8eme edition (1935)

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