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 A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...

. They allow blood vessels and nerves to travel through them to supply the

osteocyte An osteocyte, an oblate-shaped type of bone cell with dendritic processes, is the most commonly found cell in mature bone. It can live as long as the organism itself. The adult human body has about 42 billion of them. Osteocytes do not divide an ...

Structure

Each Haversian canal generally contains one or two

capillaries A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the in ...

and many

nerve fibres An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pote ...

. The channels are formed by concentric layers called lamellae, which are approximately 50 μm in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...

. The Haversian canals surround

blood vessels Blood vessels are the tubular structures of a circulatory system that transport blood throughout many animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste an ...

and

nerve cells A neuron (American English), neurone (British English), or nerve cell, is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. They are located in the nervous system and help to ...

throughout bones and

communicate Communication is commonly defined as the transmission of information. Its precise definition is disputed and there are disagreements about whether unintentional or failed transmissions are included and whether communication not only transmit ...

with

s (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 A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provi ...

its strength.

Active transport In cellular biology, active transport is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellula ...

is used to move most substances between the blood vessels and the osteocytes. Haversian canals are contained within

osteon In osteology, the osteon or haversian system (; named for Clopton Havers) is the fundamental functional unit of much compact bone. Osteons are roughly cylindrical structures that are typically between 0.25 mm and 0.35 mm in diameter. Thei ...

s, 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

Clinical significance

Fracture

Blood vessels in the Haversian canals are likely to be damaged by

bone fracture A bone fracture (abbreviated FRX or Fx, Fx, or #) is a medical condition in which there is a partial or complete break in the continuity of any bone in the body. In more severe cases, the bone may be broken into several fragments, known as a ''c ...

. This can cause

haematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...

Rheumatoid arthritis

Haversian canals may be wider in patients with

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...

. They are also more likely to contain

osteoclast An osteoclast () is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and bone remodeling, remodeling of bones of the vertebrate, vertebral skeleton. The osteoclast disassembles and digests th ...

s that break down bone structure. These differences are studied with

light microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical, el ...

History

Haversian canals were first described (and probably discovered) by

British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories and Crown Dependencies. * British national identity, the characteristics of British people and culture ...

physician A physician, medical practitioner (British English), medical doctor, or simply doctor is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through the Medical education, study, Med ...

Clopton Havers Clopton Havers (24 February 1657 – April 1702) was an English physician who did pioneering research on the microstructure of bone. He is believed to have been the first person to observe and almost certainly the first to describe what are now ...

, 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

endotherm An endotherm (from Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions inst ...

y and secondary Haversian reconstruction, this feature is absent in many living mammals (e.g.

monotreme Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified ...

s, '' Talpa'',

flying foxes ''Pteropus'' (suborder Yinpterochiroptera) is a genus of megabats which are among the largest bats in the world. They are commonly known as fruit bats or flying foxes, among other colloquial names. They live in South Asia, Southeast Asia, Austr ...

, '' Herpestes'', ''

Dasypus ''Dasypus'' is the only extant genus in the family Dasypodidae. Its species are known as long-nosed or naked-tailed armadillos. They are found in South America, South, Central America, Central, and North America, as well as on the Caribbean islan ...

'') and birds ('' Aratinga'', '' Morococcyx'', '' Nyctidromus'', '' Momotus'', '' Chloroceryle'') while others possess only scattered Haversian systems (e.g.

artiodactyls Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other thre ...

, ''

Didelphis ''Didelphis'' is a genus of New World marsupials. The six species in the genus ''Didelphis'', commonly known as Large American opossums, are members of the ''opossum'' order (biology), order, Didelphimorphia. The genus ''Didelphis'' is composed ...

'', ''

Anas ''Anas'' is a genus of dabbling ducks. It includes the pintails, most teals, and the mallard and its close relatives. It formerly included additional species but following the publication of a molecular phylogenetic study in 2009 the genus was s ...

'', '' Gallus'',

turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...

helmeted guineafowl The helmeted guinea fowl (''Numida meleagris'') is the best known of the guinea fowl bird family, Numididae, and the only member of the genus ''Numida''. It is native to Africa, mainly south of the Sahara, and has been widely introduced, as ...

). Scattered Haversian canals are also found in ectotherms like cryptodire 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

ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...

s, basal stem-mammals (e.g. ''

Ophiacodon ''Ophiacodon'' (meaning "snake tooth") is an extinct genus of synapsid belonging to the family Ophiacodontidae that lived from the Late Carboniferous to the Early Permian in North America and Europe. The genus was named along with its type specie ...

''), ''

Limnoscelis ''Limnoscelis'' (/limˈnäsələ̇s/, meaning "marsh footed") was a genus of large diadectomorph tetrapods from the Late Carboniferous to early Permian of western North America. It includes two species: the type species ''Limnoscelis paludis'' f ...

'', and

temnospondyls Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished wo ...

. When endosteal Haversian systems are considered, the phylogenetic distribution becomes even broader.

Notes

References

External links

* http://www.lab.anhb.uwa.edu.au/mb140/ * Video of haversian canal system within cortical bone.

Additional images

File:Osso por Descalcificação – HE – 40x.JPG, Bone by decalcification (40x): File:Osso por Descalcificação2 – HE – 100x.JPG, Bone by decalcification (100x): {{Bone and cartilage Skeletal system