Lamellar bone, types

This composite of tropocollagen and hydroxapatite forms fibres that unite to form fibre bundles. The fibre bundles are the building blocks of the next hierarchical layer. Depending on the bone type, the fibre bundles may be arranged irregularly, uniaxially, or in a lamellar structure, the latter structure being the one most common in adult humans. Within the lamellar bone, the fibres are arranged in parallel in layers the fibre bundles in adjacent layers are rotated relative to each other, similar to the fibre layers in a laminate (see section 9.1.1). 

Of the many structural types of bone, only the lamellar , plexiform bone in the diaphysis compacta of long bones is of importance for fluorine dating, because only this material is homogeneous enough for the development of a dominant profile that starts from the periosteal surface. Especially in haversian bone (e.g. human bone), profiles may be forming at a number of points in the bone and in a number of different directions, stemming from surfaces within the bone (e.g. Haversian canals) or from the medullary cavity. These profiles often hide the true... 

The bone matrix that comprises lamellar and woven bone contains another level of porosity on the order of 5 to 10 frm that is associated with the bone cells (see Fig. 8.2a, b, c). Osteocytes, the most common type of bone cell, are surrounded by a thin layer of extracellular fluid within small ellipsoidal holes (5 /zm minor diameter, 7 to 8 /xm major diameter) called lacunae, of which there are about 25,000 per /iim in bone tissue. The lacunae are generally arranged along the interfaces between lamellae. However, the lacunae also have a lower-scale porosity associated with them. Each osteocyte has dendritic processes that extend from the cell through tiny channels ( 0.5 /on diameter, 3 to 7 /zm long) called canaliculi to meet at cellular gap junctions with the processes of surrounding cells. There are about 50 to 100 canaliculi per single lacuna and about 1 million per mm of bone. 

At the highest hierarchical level (1 to 5 mm), there are two types of bone cortical bone, which comes as tightly packed lamellar, Haversian, or woven bone and trabecular bone, which comes as a highly porous cellular solid. In the latter, the lamellae are arranged in less well-organized packets to form a network of rods and plates about 100 to 300 /xm thick interspersed with large marrow spaces. Many common biological materials, such as wood and cork, are cellular solids. ... 

---