Chemistry Reference
In-Depth Information
of the mineral hydroxyapatite (composed of calcium hydroxy phosphate)
(Katzenberg and Harrison 1997). The complex composite material created by
the intimate blend between collagen and carbonated calcium phosphate max-
imizes the ratio between the strength and the weight of bone and optimizes
its load-bearing qualities. Thus, although the whole skeleton makes up only
about 15% of the total weight of the human body, the bones of the skeleton
provide practically all of the mechanical support that the body requires
(Sandford 1993; Woodhead and Galloway 1980).
Visual examination of fresh bone reveals two major components: an
outer layer of hard compact matter that makes up the casing of the bone,
and inside, blending with the casing, cancellous, spongy tissue having a fine,
loose structure. In long bones, such as those of the arms and legs, the spongy
tissue makes up the internal part of the bone, including the marrow, as
illustrated in Figure 78. The thickness of the hard, dense casing varies in
FIGURE 78
Bone; longitudinal and transversal cross sections.
Bone, the dense,
rigid tissue that composes the skeletons of mammals, is made up of a matrix of soft
organic matter impregnated with a hard bioinorganic substance. The organic matrix
consists mainly of collagen fibers mixed with lesser amounts of fats. The impregnating
bioinorganic component is carbonated hydroxyapatite, which imparts rigidity to bone.
Macroscopically, two varieties of bone tissue can be distinguished: compact bone and
cancellous (spongy) bone; compact bone, made up primarily of carbonated hydroxya-
patite forms the exterior mass of the long bones and the surface layers of others. Can-
cellous bone, a soft, pulpy tissue that consists mainly of fat and collagen, fills up the
interior of short and flat bones and also the ends of long bones. The illustration shows
longitudinal
(a)
and transversal
(b)
cross sections of a long bone.
