What Is Meant by Bone Ossification?
Bone ossification, also called osteogenesis, is the bone formation process. Ossification usually starts in the sixth or seventh week of embryonic development and continues until the person is about 25 years old. But this may vary depending on the individual. There are two forms of bone ossification, They are:
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Intramembranous ossification.
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Endochondral ossification.
This process usually begins with mesenchymal tissue precursors, but the process of bone development differs. In the case of intramembranous ossification, the mesenchymal tissue is directly converted into bone structures such as the flat bone structure of the clavicle, skull, or cranial bones. In the case of endochondral ossification, the mesenchymal tissue is converted into cartilage, which is then replaced by a bony structure, which usually forms the long bone.
What Is Meant by Osteoblast?
Osteoblasts are cells responsible for the deposition of the bone and the regulation of osteoclast cells. These cells are derived from mesenchymal stem cells. At the time of the embryonic phase, osteoid is secreted which is an unmineralized matrix. This is calcified and results in bone formation. These osteoblast cells play an important role in bone formation and resorption.
What Is Meant by Osteoclast?
Osteoclast are multinucleated cells that are involved in the bone resorption process. They are produced from macrophages. These enter the bone structure through blood vessels. Each osteoclast has many processes that extend into the matric and help in the secretion of the hydrogen ions, which results in acidification and bone breakdown. Osteoclast functioning is under strict control. Overactivity of osteoclasts can result in osteoporosis; at the same time, reduced activity can cause osteopetrosis.
What Is Meant by Osteocytes?
Osteocytes are cells that are present in huge numbers in the body. These cells are produced from osteoblasts, which are trapped within the osteons. The primary function of these cells is mechanosensation. Cytoplasmic processes are used to connect osteocytes to other environments. The communication with other osteocyte cells and the surrounding environment helps them to rule out stress and deformation of the bone structures. Based on this information, these cells are used in bone remodeling.
How Is Bone Developed?
Three derivatives can track the skeletal development, these are:
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Cranial Neural Crest Cells:
These are from the flat bones of the skull, cranial bone, and clavicle.
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Somites:
These are from the remains of the axial skeleton.
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Lateral Plate Mesoderm:
These are used in the formation of long bones.
Bone formation usually requires a template for further development. This template is usually the cartilage, which is from the embryonic mesoderm. But in the case of intramembranous ossification, undifferentiated mesenchyme is included. This is the framework that determines bone development. By the time of birth, almost all the cartilage will be replaced by the bone. The process of ossification will continue throughout the growth until the age of mid-twenties.
How Does Bone Growth Take Place?
Bone usually grows in length at the epiphyseal plate through a process similar to endochondral ossification. The cartilage at the epiphyseal plate region next to the epiphysis tends to grow through mitosis.
What Is Meant by Intramembranous Ossification?
Intramembranous ossification is the process where there is direct conversion of mesenchyme into the bone. This process starts when the neural crest-derived mesenchyme cells develop and differentiate into specialized bone-developing cells called osteoblast. These osteoblasts form clusters and develop an ossification center. The osteoblast starts to produce osteoid. These are unmineralized collagen proteoglycan matrices that help bind calcium. This process of calcium binding to the osteons can cause hardening of the matrix, and the osteoblast gets entrapped. This entrapment of osteoblast results in the conversion of osteoblast into osteocytes. As the osteoblasts produce osteoid continuously, they usually surround the blood vessels, forming spongy, cancellous, or trabecular bony structures. These vessels then will usually result in the formation of red bone marrow. The mesenchymal cells present over the bone result in the formation of a membrane called periosteum. Cells present on the inner area of the periosteum differentiate to form osteoblasts, which then produce osteons in the presence of the existing matrix, which results in the formation of layers. These layers are usually called compact or cortical bones.
The summary of this process is:
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The mesenchymal cells differentiate into osteoblast cells. These form the ossification centers.
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Osteoid entraps the osteoblast cells formed. These cells are transformed into osteocytes.
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Formation of trabecular bone and periosteum takes place.
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Cortical bone formation takes place on the superficial surface of the trabecular bone.
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Blood vessels will be involved in the formation of red marrow.
Which Are the Bones That Develop Through the Intramembranous Ossification Process?
Some of the bones which develop through the intramembranous ossification process are:
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Development of flat bones of the embryo such as mandible, maxilla, skull, pelvis, subperiosteal regions of the long bone, and clavicle,
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Bone formation through distraction osteogenesis makes longer bone out of shorter bone.
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Blastema bone is seen in children with amputation.
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Healing of fracture with rigid fixations such as compression plates.
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Healing of one component with intramedullary nailing.
What Is Meant by Endochondral Ossification?
Endochondral ossification is one of the ossification methods through which the bone develops. In the case of endochondral ossification, the bone is initially replaced by hyaline cartilage. The mesenchymal cells differentiate to form chondrocytes, which forms the cartilage of the bone. These chondrocytes enable mineralization. Chondrocytes undergo apoptosis and bring osteogenic cells. The bone will replace this cartilage in the later stages. These usually are involved in the formation of long bone structures.
Conclusion
Ossification is the bone formation process. This process usually begins at the sixth or seventh week of the embryo and continues until the individual reaches the age of 25 years. There are two forms of ossification: endochondral ossification and intramembranous ossification. Intramembranous ossification usually occurs through direct conversion of mesenchymal cells into bony structures.
