Ossification - Wikipedia Ossification This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( May 2011 ) Parts of this article ( those related to PMID 24292720 ) need to be updated. Please update this article to reflect recent events or newly available information. ( December 2013 ) Look up ossification in Wiktionary, the free dictionary. Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine ( TGF - β, IGF ) signalling. Ossification ( or osteogenesis ) in bone remodeling 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 : 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 internal fixation with metal plates, screws, pins, rods and nails 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. Contents 1 Timetable for human ossification 2 Intramembranous ossification 3 Endochondral ossification 4 Evolution 5 See also 6 References Timetable for human ossification Time period Bones affected Third month of fetal 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 ossification 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 Intramembranous ossification Intramembranous ossification forms the flat bones of the skull, clavicle and mandible. Endochondral ossification Endochondral ossification is the formation of long bones and other bones. This requires a hyaline cartilage precursor. There are two centres of ossification for endochondral ossification. The primary centre In long bones, bone tissue first appears in the diaphysis ( middle of shaft ). Chondrocytes multiply and form trebeculae. Cartilage is progressively eroded and replaced by hardened bone, extending towards the epiphysis. A perichondrium layer surrounding the cartilage forms the periosteum, which generates osteogenic cells that then go on to make a collar that encircles the outside of the bone and remodels the medullary cavity on the inside. The nutrient artery enters via the nutrient foramen from a small opening in the diaphysis. It invades the primary centre of ossification, bringing osteogenic cells ( osteoblasts on the outside, osteoclasts on the inside. ) The canal of the nutrient foramen is directed away from more active end of bone when one end grows more than the other. When bone grows at same rate at both ends, the nutrient artery is perpendicular to the bone. Most other bones ( e.g. vertebrae ) also have primary ossification centres, and bone is laid down in a similar manner. Secondary centres The secondary centres generally appear at the epiphysis. Secondary ossification mostly occurs after birth ( except for distal femur and proximal tibia which occurs during 9th month of fetal development ). The epiphyseal arteries and osteogenic cells invade the epiphysis, depositing osteoblasts and osteoclasts which erode the cartilage and build bone. This occurs at both ends of long bones but only one end of digits and ribs. Primary center of ossification, or Growth Plate. Evolution A spotted gar larva at 22 days stained for cartilage ( blue ) and bone ( red ). 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. However, other possibilities include bony tissue evolving as an osmotic barrier, or as a protective structure. See also Dystrophic calcification Mechanostat, a model describing ossification and bone loss Ossicone, the horn - like ( or antler - like ) protuberances on the heads of giraffes and related species Osteogenesis imperfecta, a juvenile bone disease Fibrodysplasia ossificans progressiva, an extremely rare genetic disease which causes fibrous tissue ( muscle, tendon, ligament etc. ) to ossify when damaged Primrose syndrome, a rare genetic disease in which cartilage becomes ossified. References Jump up ^ Caetano - Lopes J, Canhão H, Fonseca JE ( 2007 ). `` Osteoblasts and bone formation ''. Acta reumatológica portuguesa. 32 ( 2 ) : 103 -- 10. PMID 17572649. ^ Jump up to : Emily Morey - Holton. `` Predicting Height from the Length of Limb Bones ''. Examining Effects of Space Flight on the Skeletal System. Moffett Field, California : NASA Ames Research Center. Archived from the original on 2012 - 03 - 01. Jump up ^ Donoghue PC, Sansom IJ ( 2002 ). `` Origin and early evolution of vertebrate skeletonization ''. Microsc. Res. Tech. 59 ( 5 ) : 352 -- 72. PMID 12430166. doi : 10.1002 / jemt. 10217. Wikimedia Commons has media related to Ossification. Bone and cartilage Cartilage perichondrium fibrocartilage callus metaphysis Cells chondroblast chondrocyte Types hyaline elastic fibrous Bone Ossification Primary bone intramembranous endochondral Cells osteoblast osteoid osteocyte osteoclast Types cancellous cortical Regions subchondral bone epiphysis epiphyseal plate / metaphysis diaphysis Condyle Epicondyle Structure Osteon Haversian canals Volkmann 's canals connective tissue endosteum periosteum Sharpey 's fibres enthesis lacunae canaliculi trabeculae medullary cavity bone marrow Shapes long short flat irregular sesamoid Physiology of bone and cartilage Bone Bone density Bone remodeling Bone healing Bone resorption Osseointegration Ossification Osteolysis Bone age Periosteal reaction Cartilage Chondrogenesis Joint Range of motion Teeth Mastication Cementogenesis Development of bone Ossification Triradiate cartilage Limb development Limb bud Apical ectodermal ridge Zone of polarizing activity Sclerotome Myotome Septum transversum Retrieved from `` https://en.wikipedia.org/w/index.php?title=Ossification&oldid=791885321 '' Categories : Animal physiology Skeletal system Tissues ( biology ) Hidden categories : Articles needing additional references from May 2011 All articles needing additional references Wikipedia articles in need of updating from December 2013 All Wikipedia articles in need of updating Talk Contents About Wikipedia Български Čeština Deutsch Español Français Bahasa Indonesia Italiano Қазақша Lietuvių Nederlands 日本 語 Polski Română Русский Slovenčina کوردی Svenska ไทย اردو 中文 Edit links This page was last edited on 23 July 2017, at 02 : 17. 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Question: when do the bones of the sternum become completely ossified
Answer: 23 to 25 years