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A schematic for long bone endochondral ossification. In developing bones, ossification commences within the primary ossification center located in the center of the diaphysis (bone shaft), [5] where the following changes occur: The perichondrium surrounding the cartilage model transforms into the periosteum. During this transformation, special ...
Endochondral ossification is the process by which most vertebrate axial skeletons form into hardened bones from cartilage. This process begins with a cartilage anlage where chondrocyte cells will congregate and start their maturation process.
Diagram showing stages of endochondral ossification. Endochondral ossification is the formation of long bones and other bones. This requires a hyaline cartilage precursor. There are two centers of ossification for endochondral ossification. The primary center. In long bones, bone tissue first appears in the diaphysis (middle of shaft).
Early in fetal development, the greater part of the skeleton is cartilaginous. This temporary cartilage is gradually replaced by bone (endochondral ossification), a process that ends at puberty. In contrast, the cartilage in the joints remains unossified during the whole of life and is, therefore, permanent. [citation needed]
The Haversian system forms during the process of endochondral ossification, which starts with a cartilage template that is gradually replaced by bone tissue. Osteoblasts, the bone-forming cells, secrete the organic components of bone matrix [osteoid] and then initiates its mineralization.
An ossification center is a point where ossification of the hyaline cartilage begins. The first step in ossification is that the chondrocytes at this point become hypertrophic and arrange themselves in rows. [1] The matrix in which they are imbedded increases in quantity, so that the cells become further separated from each other.
[6] TGF-β determines and regulates cell lineages during endochondral ossification through Sox9 and Runx2 signalling pathways. TGF-β will act as a stimulator of chondrogenesis, and an inhibitor of osteoblastic differentiation, by blocking the Runx2 factor through Smad3 activation. Sox9 stimulates differentiation into chondrocytes.
[1] The bones that form the base and facial regions of the skull develop through the process of endochondral ossification. In this process, mesenchyme accumulates and differentiates into hyaline cartilage, which forms a model of the future bone. The hyaline cartilage model is then gradually, over a period of many years, displaced by bone.