Ossification
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 |
Evolution
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
References
- ^ Caetano-Lopes J, Canhão H, Fonseca JE (2007). "Osteoblasts and bone formation". Acta reumatológica portuguesa 32 (2): 103–10. PMID 17572649.
- ^ 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
- ^ 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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Ossification
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noco/cong/tumr, sysi/epon, injr
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noco(arth/defr/back/soft)/cong, sysi/epon, injr
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dent, proc (endo, orth, pros)
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noco/cong/tumr, sysi/epon, injr
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