|MadSci Network: Anatomy|
Hi, Molly, Good question, but thereís no really good answer, Iím afraid. The pelvis is the last bone to FINISH the long and slow process of ossification, but itís not the last to BEGIN to be ossified. Ossification of the pelvis begins before youíre born, while there are still many bones that havenít even started to become mineralized, like several in your wrist and in other places. The pelvis grows a tremendous amount as you reach your final size, and itís big and very complicated. There are bone cells secreting bone matrix (mostly made of proteins, especially collagen) right up until you finish growing (and afterward, too, during the slow, lifelong process of bone remodeling). Bone can only become mineralized after the matrix is laid down. While the first phase of mineralization happens fairly quickly Ė within days to a few weeks Ė at first this mineralization just isnít as dense as it will eventually become. That takes longer, and the pelvis is the last bone to reach full mineral density, which is the reason for the statement in the previous answer you wrote in about. Paul Odgren, PhD Dept of Cell Biology University of Massachusetts Medical School Worcester
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