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The following bones develop in humans via Intramembranous ossification: [3] Flat bones of the face; Most of the bones of the skull; Clavicles; Other bone that formed by intramembranous ossification are: cortices of tubular and flat bones as well as the calvaria, upper facial bones, tympanic temporal bone, vomer, and medial pterygoid process. [4]
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).
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.
It usually consists of only endochondral ossification. Sometimes, intramembranous ossification occurs together with endochondral ossification. Intramembranous ossification, mediated by the periosteal layer of bone, occurs with the formation of callus. For endochondral ossification, deposition of bone only occurs after the mineralised cartilage.
The posterior fontanelles ossify within 6–8 weeks after birth. This is called intramembranous ossification. The mesenchymal connective tissue turns into bone tissue. Anterior fontanelle is a diamond-shaped membrane-filled space located between the two frontal and two parietal bones of the developing fetal skull. It persists until ...
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.
Intramembranous ossification is the direct ossification of mesenchyme as happens during the formation of the membrane bones of the skull and others. [8] During osteoblast differentiation, the developing progenitor cells express the regulatory transcription factor Cbfa1/Runx2. A second required transcription factor is Sp7 transcription factor. [9]
Ossification is started by the formation of layers of undifferentiated connective tissue that hold the area where the flat bone is to come. On a baby, those spots are known as fontanelles . The fontanelles contain connective tissue stem cells , which form into osteoblasts , which secrete calcium phosphate into a matrix of canals.