Biomedical Engineering Reference
In-Depth Information
Capillary or arteriole
Venule
Central canal of the
Haversian system
Concentric lamellae
forming compact bone
Artery
Trabeculae forming
spongy bone
Vein
FIGURE 11.2
Schematic of the structure of compact bone. Compact bone is formed from multiple Haversian
canal systems that are composed of concentric lamellae. Each Haversian canal has its own venule and capillary
(possible arteriole) to provide the osteocytes with nutrients and oxygen. On the interior surface of the compact
bone, trabeculae can be found to form a spongy bone marrow within long bones. Osteocytes can be found
between the lamellae (black ovals on figure), within a lacuna.
Adapted from Martini and Nath (2009).
concentric circles found within a tree trunk. Lacunae are found in between individual
lamellae and not within one lamella. Within each Haversian canal are the blood vessels
that supply the bone with nutrients. Typically, there is one capillary (or arteriole) and one
venule within each canal. Canaliculi run perpendicular to the Haversian canal and connect
the lacunae to the blood supply and other lacunae. The canaliculi can penetrate through
lamellae to connect bone cells and to aid in nutrient transport. Because the Haversian sys-
tem is fairly circular, neighboring systems do not align perfectly with one another. This
open space is filled with interstitial lamellae, which is leftover bone matrix from older
Haversian systems that have been degraded.
The outer surface of bone is covered by a structure called the periosteum, and the inner
surface of bone is covered by the endosteum. The periosteum is a fibrous membrane that
isolates bone from other tissue. Within joints, the periosteum is continuous with the sur-
rounding connective tissue. The endosteum is a cellular layer that lines the marrow cavity
of bone. This layer participates in bone growth and repair and consists of osteoprogenitor
cells. In some locations, the endosteum layer is not complete. Here the bone matrix is
exposed, and osteoblasts and/or osteoclasts can be found that are actively forming or
degrading bone.
In trabecular bone, lamellae do not form a structural unit similar to the Haversian sys-
tem seen in compact bone. Instead the bone is composed of many thin tubes termed tra-
beculae, which resemble a branching network. There is no direct blood supply to the cells
within these trabeculae. Nutrients must be transported through the canaliculi system that
is connected to another blood supply that can be far from the bone cells. Trabecular bone
is adapted to withstand stresses in many orientations, but the majority of the trabeculae
are oriented along the major stress-loading directions. The trabeculae are branched and
interconnected to distribute the loads and to be able to withstand stresses in non-major
directions. Trabecular bone is lighter than compact bone and therefore reduces the overall
weight of the bone. Also, some trabecular bone houses the red and the yellow marrow.
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