Two main forms of ossification occur in different bones, intramembranous (eg skull) and endochondral (eg vertebra, limbs) ossification. Bones within the limb form by endochondrial ossification (begins Carnegie stage 18) throughout embryo.
Endochondral Ossification in the limb
The adult human skeleton has about 206 different bones which are formed from fusion of significantly more bones in the postnatal developing neonate and child (about 275) (More? Human Bone). Ossification in general continues postnatally, through puberty until mid 20s.
The two major parts of the human skeleton are the axial (80 bones in skull, vertebra, ribs, sternum) and appendicular (126 bones in limbs, shoulders, pelvis) skeletons.
Endochondral Ossification in the limb
Endochondral Ossification in the skull base (cartilage matrix blue, bone matrix red)
Endochondral Ossification interface between dying cartilage and newly forming bone in the skull base (cartilage matrix blue, bone matrix red)
Agoston H, Khan S, James CG, Gillespie JR, Serra R, Stanton LA, Beier F. C-type natriuretic peptide regulates endochondral bone growth through p38 MAP kinase-dependent and -independent pathways. BMC Dev Biol. 2007 Mar 20;7(1):18
"C-type natriuretic peptide (CNP) has recently been identified as an important anabolic regulator of endochondral bone growth, but the molecular mechanisms mediating its effects are not completely understood. ...Our data identify novel target genes of CNP and demonstrate that the p38 pathway is a novel, essential mediator of CNP effects on endochondral bone growth"
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The process of human skeleton development begins as a cartilagenous or membranous template in the embyro, replacement by ossification through fetal development continuing into the postnatal period where many bone "pieces" fuse into puberty with a burst of growth, into young adult where many bones finally fuse. (More? Human Bone)
The process of bone formation is never completely over, with many bones continuously undergoing remodeling and providing a key repository/store for essential minerals (calcium, phosphorous).
Please email Dr Mark Hill if you wish to make a comment about this current project.