Essay Example on Bone Composition & Development: A Comprehensive Guide

Bone tissue is the semi-rigid, porous, connective tissue that supports the framework of the body. The classification of bones is made on their shapes, such as long, short, sesamoid, irregular, and flat bones. This paper seeks to explain the various bone composition and the physiological changes that occur in bone development, both in prenatal and postnatal life.

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Bones are made of an organic matrix and inorganic mineral components. The organic components are water, protein material such as collagen and chondroitin sulfate, while the inorganic has minerals such as calcium, phosphate and lead. I Bones have two major parts, the periosteum on the outside, and endosteum on the inside. Its functional unit is the osteon.

Ossification depends on the bone type. Flat bones form through intramembranous ossification, while the long bones are formed through endochondral ossification. Bones also form condensation models of mesenchyme, which are controlled through genetic mediators such as bone morphogenic pointers five, growth factor 5 and transforming growth factor. These control both proliferation and apoptosis of cells. Finally, three major types of cells involved in ossification are osteoclasts, osteoblasts, osteocytes cells.

Intramembranous ossification begins during the sixth week, where mesenchyme becomes vascular in nature, and forms osteoblasts (Moore & Persaud & Torchia, 2018). The cluster of osteoblasts forms an osteoblastic centre, which then creates the osteoid. The osteoid is composed of an unmineralized matrix that hardens when calcium phosphate and other salts are deposited. As the osteoid hardens, the osteoblasts are trapped and form osteoclasts, which are later responsible for bone resorption in adulthood (Breeland & Menezes, 2019). The osteoid also calcifies and forms small, needle-like structures of spongy bone, called spicules. Spicules then aggregate in the form of small supporting beams called trabeculae. Trabeculae then form the meshwork of primitive bone. Once the blood vessels condense with the outer osteoblasts, they condense and form the periosteum, which is the sheath that covers the bone. The condensation of trabeculae forms woven bone which is the first sign of bone ossification. It appears disorganized and weak (Moore & Persaud & Torchia, 2018).

Eventually, woven bone is replaced by a stronger bone called lamellar bone. Lamellae are also strong and regular in pattern. Concentric lamellae also develop around blood vessels, thus forming canals called osteons, where blood vessels and nerves pass through the bone (Moore & Persaud & Torchia, 2018). This allows nutrient supply. It has regular and parallels arranged strong sheets of bone. Between the surface plates of lamellae, the interconnecting bones remain as speculates, and don't harden. This remains as spongy bone. Finally, between the spongy bones, the mesenchyme forms bone marrow. Most bones are ossified by birth aside from the skull and the collar bone, to allow for passage during birth (Moore & Persaud & Torchia, 2018).

Endochondral ossification begins with the initial laydown of hyaline cartilage, which is then replaced by bone tissue (Breeland & Menezes, 2019). The process of ossification begins during the sixth week as well, where mesenchyme begins to form cartilage, chondrocytes and the rod-like structure, with the perichondrium on the outside. In the diaphysis, chondrocytes enlarge and begin resorbing the matrix and calcifies. The hardening of chondrocytes leads to their death due to the lack of nutrient supply (Soames, 2018). Stem cells separate from the perichondrium and begin to differentiate and form osteoblasts, which then form a distinct layer called the periosteal collar around the cartilage shaft. A periosteal bud, consisting of capillaries and osteoblasts, invades the core of the cartilaginous shaft forming the primary ossification centre. The remains of the calcified cartilage remain as a template onto which osteoblasts can now build bone. Bone development extends towards the epiphyses from the centre and takes place around the 12th week (Moore & Persaud & Torchia, 2018).

The same process in the diaphysis happens in the epiphyses, now called secondary ossification centres. Spongy bone is formed at the epiphyses. Osteoclasts resorb bone in the diaphysis, creating the medullary cavity (Moore & Persaud & Torchia, 2018). Here, all cartilage except at the articular surfaces has been replaced. A distinct area also separates the epiphyses, and the diaphysis, which is called the epiphyseal plate.

Bone growth in adulthood occurs at the epiphyseal plate (Allen & Burr, 2019). It has the uppermost zones, the reserve/resting zone which provides attachment to the, and the proliferative zone, which multiply via mitosis and supplies chondrocytes to the zone of maturation and hypertrophy. The zone of hypertrophy allows the maturation and multiplication of chondrocytes to supply the zone of calcification below it. The zone of calcification has mature chondrocytes that have calcified and are dead. The osteoblasts form the diaphysis, penetrate this area, and provide osteoblasts on top of the calcified cartilage increasing bone length. Bones grow until late adulthood, where the chondrocytes are replaced by bone tissue, and an epiphyseal line replaces the plate. Appositional growth occurs by osteoclasts resorbing old bone and replacing it with new osteoblastic activity. This increases the medullary cavity, as well as the diaphysis diameter.

Conclusion

In summary, bones compose the skeleton framework that supports tissues in the human body. The composition of bone is both organic and inorganic in nature. Bone formation occurs through endochondral ossification, which requires the laydown of cartilage which is then replaced by osseous tissue, while intramembranous uses mesenchyme to build bone tissue de novo. The growth of bone tissue occurs both in length and diameter. At the epiphyseal plate, continuous deposition of chondrocytes that ossify lengthens the bone in diameter, while I apposition, osteoclast activity resorbs bone, and osteoclasts replace it increasing diameter.

References

Allen, M. R., & Burr, D. B. (2019). Bone Growth, Modeling, and Remodeling. In Basic and Applied Bone Biology (pp. 85-100). Academic Press.

Breeland, G., & Menezes, R. G. (2019). Embryology, bone ossification. In StatPearls [Internet]. StatPearls Publishing.

Moore, K. L., Persaud, T. V. N., & Torchia, M. G. (2018). The Developing Human-E-Book: Clinically Oriented Embryology. Elsevier Health Sciences.

Soames, R. W. (2018). Anatomy and Human Movement E-Book: Structure and function. Elsevier Health Sciences.