Biomedical Engineering Reference
In-Depth Information
Outer circumferential
lamellae
Interstitial
lamellae
Inner
circumferential
lamellae
Haversian systems
(osteons)
Periosteum
Trabeculae
of cancellous
bone
Blood vessels
Sharpey's
fibers
Endosteum
Haversian
canals
Volkmann's
canals
Figure 9.2
A detailed view of the structure of a typical long
bone. (From figure 2.1 of Martin
et al
.[10].)
venules (the efferent system), but unlike true capillaries, they apparently are not able
to change diameter in response to physiologic needs [11]. Diffusion from Haversian
vessels to the bone cells buried in the bony matrix is insufficient to maintain their
nutrition; convection driven by the interstitial fluid pressure gradients is necessary
for the viability of these cells. Canaliculi serve to connect osteocytic processes
[12]. Increased distance from the vascular source (the Haversian artery) probably
accounts for the finding that the interstitial bone is more susceptible to ischemia
than is the Haversian bone [13].
9.2.2
Dynamics of the Arterial System
In considering the hemodynamics of any tissue, the important elements to be
considered are fluid and tissue pressures, fluid viscosity, vessel diameter, and the
capillary bed. Blood vessels in a bone are richly supplied with nerves and are
intimately connected to vasomotor nerve endings; these nerves presumably exert
a precise control over blood flow in the bone [14]. It is known that in most soft
tissues, the arteriolar mechanism reduces the blood pressure from 90 mmHg or
more in arteries to about 35 mmHg at the arterial end of capillaries. Arterial vessels
will close unless the transmural pressure is positive, that is, to say, unless the blood
