Bones are living and rigid tissue, that form the skeleton of the body. It form the main supporting framework of the body, produce red and white blood cells, store minerals, provide support and protect the various organs of the body.
In the human body at birth, there are over 270 bones,but many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small sesamoid bones. The largest bone in the body is the femur or thigh bone and the smallest is the stapes in the middle ear.
DIVISION OF SKELETAL SYSTEM-
Axial skeleton
The axial skeleton (80 bones) is formed by the
- Vertebral column(26)
- A part of the rib cage (12 pairs of ribs and the sternum), and
- The skull (22 bones and 7 associated bones).
The upright posture of humans is maintained by the axial skeleton, which transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at the hip joints.
Appendicular skeleton
The appendicular skeleton (126 bones) is formed by the
- Pectoral girdles,
- The upper limbs,
- The pelvic girdle or pelvis, and
- The lower limbs.
Their functions are to make locomotion possible and to protect the major organs of digestion, excretion and reproduction.
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Bones in the human skeleton
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| Axial skeleton |
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| Appendicular |
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COMPOSITION OF BONE-
Bone itself consists mainly of collagen fibers and an inorganic bone mineral in the form of small crystals. Bone has an 1/3 organic component of mainly collagen fiber called ossien [connective tissue] and 2/3 inorganic component of bone mineral made up of various salt.
The inorganic component make it hard and rigid, which can afford resistance to compressive forces of weight-bearing and impact forces of jumping.
The organic connective tissue (collagen fibers) make it tough and resilient [flexible], which can afford resistance to tensile forces. In strength, bone is comparable to iron and steel.
In vivo bone ( living bone in the body) contains between 10% and 20% water, Of its dry mass approximately 60-70% is bone mineral. The composition of bone mineral is much more complex and contain calcium phosphate, calcium carbonate or additional ions such as silicon, carbonate and zinc.
DEVELOPMENT OF BONE
The formation of bone is called ossification. During the fetal stage of development this occurs by two processes: intramembranous ossification and endochondral ossification.
- Intramembranous ossification involves the formation of bone from connective tissue,
- endochondral ossification involves the formation of bone from cartilage.
Intramembranous ossification
Mainly occurs during formation of the flat bones of the skull but also the mandible, maxilla, and clavicles; the bone is formed from connective tissue such as mesenchyme tissue rather than from cartilage.
The process includes: the development of the ossification center, calcification, trabeculae formation and the development of the periosteum.
Endochondral ossification
occurs in long bones and most other bones in the body; it involves the development of bone from cartilage. This process includes the development of a cartilage model, its growth and development, development of the primary and secondary ossification centers, and the formation of articular cartilage and the epiphyseal plates.
CLASSIFICATION OF BONE