The major constituent of the is the bone matrix. Woven and lamellar bone are the terms based on the microscopic differentiation of the bone. Bone is formed by the hardening of this matrix entrapping the cells. For example, when are trapped in the matrix, they become osteocytes.
The inorganic is mainly crystalline mineral salts and calcium and the organic part of the matrix is mainly composed of Type I collagen.
[More on bone anatomy and physiology]
On the microscope, two types of bone can be identified.
These bones differ in the pattern of collagen forming the osteoid.
Woven bone is characterized by haphazard organization of collagen fibers and is mechanically weak.
Woven bone is produced when osteoblasts produce osteoid rapidly.
It is present in
- All fetal bones initially when the bone is laid down. Later it gets replaced by lamellar bone.
- After fractures, the initial bone that unites the fracture is woven bone. It too gets replaced by lamellar bone.
- Paget’s disease.
Woven bone is weaker, with a smaller number of randomly oriented collagen fibers, but forms quickly. It has been named due to the woven appearance of the fibrous matrix.
Woven bone is basically either immature bone or pathologic bone. It is not stress oriented. Compared to the lamellar bone, woven bone has more osteocytes per unit of volume and higher rate of turnover.
Woven bone is weaker and flexible than lamellar bone.
Lamellar bone is secondary bone created by remodeling of woven bone. Lamellar bone has a regular parallel alignment of collagen into sheets (lamellae) and is mechanically strong. It is highly organized in concentric sheets with a much lower proportion of osteocytes to surrounding tissue. Lamellar bone is stronger and filled with many collagen fibers parallel to other fibers in the same layer (osteons).
In cross-section, the fibers run in opposite directions in alternating layers. This kind of structural arrangement assists in the bone’s ability to resist torsion forces.
Note: A microscope is necessary to differentiate between the two.
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