Biology Reference
In-Depth Information
point for further study:
Enlow (1963), Martin and Burr (1989), Carter and Beaupre (2001)
, and
Hall (2005)
.
Bone Biology
Bone is a very dynamic tissue (
Enlow, 1963; Martin and Burr, 1989; Carter and Beaupre,
2001; Hall, 2005
). It functions to provide mechanical support, protect vital structures, aid
in hematopoiesis (generation of blood cells), and maintain mineral homeostasis.Itis
a composite material with both organic and inorganic components including a collagen
matrix comprised of hydroxyapatite crystals.
To comprehend the structure and function of bone, it is necessary to grasp the types of cells
involved in cortical bone modeling and remodeling. Bone modeling involves the sculpting
of bone during growth and development. New bone, or primary bone, is produced or
resorbed as individuals grow and there are shifts in areas of stress and strain being placed
on the bone (
Enlow, 1963
). Modeling induces cortical bone changes in length and in width
depending on the location and function of the type of bone.
Bone remodeling involves the removal and replacement of old bone with new bone.
Enlow
(1963)
discusses this remodeling process of bone growth as a systematic coordination
between bone building cells (osteoblasts) and bone resorbing cells (osteoclasts). Bone
remodeling occurs throughout life at differing rates. This normal process is often affected
by age and pathological, or inflammatory processes (
Recker, 1983; Hall, 2005
), and results
in secondary bone. These terms and processes will be elaborated upon in subsequent sections
in this chapter.
Bone Function
Bone is enveloped by two membranes. The periosteum, a double-layered protective
covering on the outer bone surface, is comprised of a fibrous layer of dense cartilaginous
tissue surrounding an inner osteogenic layer composed of osteoblasts and osteoclasts.
This layer is rich in nerve fibers, blood, and lymphatic vessels and is secured to the bone
via Sharpey's fibers. The endosteum is a membranous layer lining the internal surface of
the medullary cavity. Bone modeling or remodeling can occur on either the periosteal or
endosteal surfaces (
Frost, 1963, 1964; Lacroix, 1971; Ortner, 1975; Recker, 1983; Martin and
Burr, 1989; Martin et al., 1998
).
There are two general types of human bone: compact or cortical bone and spongy or
trabecular bone. The cortical bone is the outer layer and is harder and denser than the inner
spongy bone (
Recker, 1983; Martin and Burr, 1989; Carter and Beaupre, 2001; Hall, 2005
). The
cortical and trabecular bone lies between the periosteum and endosteum. Cortical bone is
primarily found in varying thicknesses in the shafts, or diaphyses, of long bones, and
surrounding the trabeculae. The organization of cortical and trabecular bone allows for
maximum absorption of energy with minimal trauma to the bone structure itself (
Martin
and Burr, 1989
).
Spongy bone is located within the medullary cavity as well as in the ends of long bones,
inside the bodies of vertebrae, and between cortical bone layers in the flat bones of the
cranium (
Recker, 1983; Martin and Burr, 1989; Carter and Beaupre, 2001; Hall, 2005
).
