Haversian canals (sometimes canals of Havers, osteonic canals or central canals) are a series of microscopic tubes in the outermost region of bone called cortical bone. They allow blood vessels and nerves to travel through them to supply the .
Structure
Each Haversian canal generally contains one or two
capillary and many
nerve fibres. The channels are formed by concentric layers called lamellae, which are approximately 50 μm in
diameter. The Haversian canals surround
blood vessels and
nerve cells throughout bones and communicate with
(contained in spaces within the dense bone matrix called lacunae) through connections called canaliculi. This unique arrangement is conducive to mineral salt deposits and storage which gives
bone tissue its strength.
Active transport is used to move most substances between the blood vessels and the osteocytes.
Haversian canals are contained within , which are typically arranged along the long axis of the bone in parallel to the surface. The canals and the surrounding lamellae (8-15) form the functional unit, called a Haversian system, or osteon.
Clinical significance
Fracture
Blood vessels in the Haversian canals are likely to be damaged by
bone fracture.
This can cause
Hematoma.
Rheumatoid arthritis
Haversian canals may be wider in patients with rheumatoid arthritis.
They are also more likely to contain
that break down bone structure.
These differences are studied with
Microscopy.
History
Haversian canals were first described (and probably discovered) by
England physician Clopton Havers, after whom they are named.
He described them in his 1691 work
Osteologica Nova.
In different animals
Human bones are densely vascularized as in many other mammals. Even though some authors tried to identify a correlation between
and secondary Haversian reconstruction, this feature is absent in many living mammals (e.g.
,
Talpa,
Pteropus,
Herpestes,
Dasypus) and birds (
Aratinga,
Morococcyx,
Nyctidromus,
Momotus,
Chloroceryle) while others possess only scattered Haversian systems (e.g. artiodactyls,
Didelphis,
Anas,
Junglefowl, turkey, helmeted guineafowl). Scattered Haversian canals are also found in ectotherms like
Cryptodira turtles.
Among extinct groups, dense Haversian vascularization is only present in stem-birds (dinosaurs) and stem-mammals (therapsids)
while scattered Haversian systems can be found in
,
, basal stem-mammals (e.g.
Ophiacodon),
Limnoscelis, and
Temnospondyli. When
Endosteum Haversian systems are considered, the phylogenetic distribution becomes even broader.
Notes
External links
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http://www.lab.anhb.uwa.edu.au/mb140/
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Video of haversian canal system within cortical bone.
==Additional images==
