Bone and Cartilage – its Structure and Physical Properties - Biomechanics of Hard Tissues - page 22

Figure 1.11 The spongy bone in histological section. The
trabecules are surrounded by the marrow, and white spheres
of fat in the marrow are seen. Courtesy of Litwin and Gajda.
it grows, it ossifies near the diaphysis and the epiphyses. At about 18-25 years of
age, the metaphysis stops growing and completely ossifies into a solid bone.
The interior of the bone is known as the spongy bone (or cancellous or trabecular
bone), cf. Figures 1.10b and 1.11. Spongy tissue has porous appearance and is
composed of a network of trabecules, and rod- and plate-like elements that make
the tissue lighter and allow space for blood vessels and marrow. Spongy bone
accounts for 20% of the total bone mass, but (from macroscopic point of view) has
nearly 10 times the surface area of compact bone.
1.3
Microscopic Structure of the Bone
1.3.1
General
Bone is composed of three major components: (i) small plate-shaped crystals of
carbonate apatite, (ii) water, and (iii) macromolecules, of which type I collagen is
the major constituent. The manner in which the crystals and the collagen fibrils
are organized in a bone has not been resolved yet. In mineralized collagen fibrils
of turkey tendon, the crystals are arranged in parallel layers across the fibrils, with
the crystal c axes aligned with the fibril lengths, and in rat bones the plate-shaped
crystals are also arranged in parallel layers within individual lamellae [76].