Editing Bone (section)

====Deposition====
The extracellular matrix of bone is laid down by [[osteoblast]]s, which secrete both collagen and ground substance. These cells synthesise collagen alpha polypetpide chains and then secrete collagen molecules. The collagen molecules associate with their neighbors and crosslink via lysyl oxidase to form collagen fibrils. At this stage, they are not yet mineralized, and this zone of unmineralized collagen fibrils is called "osteoid". Around and inside collagen fibrils calcium and phosphate eventually [[Precipitation (chemistry)|precipitate]] within days to weeks becoming then fully mineralized bone with an overall carbonate substituted hydroxyapatite inorganic phase.<ref>{{cite journal | vauthors = Buss DJ, Reznikov N, McKee MD | title = Crossfibrillar mineral tessellation in normal and Hyp mouse bone as revealed by 3D FIB-SEM microscopy | journal = Journal of Structural Biology | volume = 212 | issue = 2 | page = 107603 | date = November 2020 | pmid = 32805412 | doi = 10.1016/j.jsb.2020.107603 | s2cid = 221164596 | url = https://escholarship.mcgill.ca/concern/articles/vq27zt432 }}</ref>{{sfn|Hall|2005|p=981}}

In order to mineralise the bone, the osteoblasts secrete alkaline phosphatase, some of which is carried by [[Vesicle (biology and chemistry)|vesicles]]. This cleaves the inhibitory pyrophosphate and simultaneously generates free phosphate ions for mineralization, acting as the foci for calcium and phosphate deposition. Vesicles may initiate some of the early mineralization events by rupturing and acting as a centre for crystals to grow on. Bone mineral may be formed from globular and plate structures, and via initially amorphous phases.<ref name=r1>{{cite journal| vauthors = Bertazzo S, Bertran CA |year=2006|title=Morphological and dimensional characteristics of bone mineral crystals|journal= Key Engineering Materials|volume=309-311 |pages=3–6 |doi=10.4028/www.scientific.net/kem.309-311.3|s2cid=136883011 }}</ref><ref>{{cite journal|doi=10.4028/www.scientific.net/kem.309-311.11|title=Morphological Characterization of Femur and Parietal Bone Mineral of Rats at Different Ages|year=2006| vauthors = Bertazzo S, Bertran C, Camilli J |journal=Key Engineering Materials|volume=309–311|pages=11–14|s2cid=135813389}}</ref>