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{{for|the television series|Bones (TV series)}}
{{Infobox anatomy
|Name = Bone
|image = Foot bones.jpg
|caption = The ''bones'' of a human [[foot]]
}}
'''Bones''' are parts of the [[skeleton]] of [[vertebrate]]s. They also protect [[Organ (anatomy)|organs]] inside our body.<ref name=firstbody>{{cite book|url=https://books.google.com/books?id=weyXAAAACAAJ|title=My First Book on the Human Body|publisher=Robert Frederick|location= Bath|date=2004|isbn=0-7554-3506-0|accessdate=13 July 2010|language=}}</ref>

The bones are the [[framework]] of the [[body]]. Without them we would be a pile of organs and [[skin]] on the ground and would not be able to move.

Bones also protect us. The [[skull]] protects the [[brain]] and the [[rib cage|rib]]s protect the [[heart]] and [[lung]]s.  The [[jaw]] and [[skull]] support the facial muscles, which help us eat and move our mouth.  The [[pelvis]] protects the reproductive organs, and [[vertebrae]] protect the [[spinal cord]].  

Bone is living tissue, and must be maintained by taking regular [[exercise]] and by having [[calcium]] from foods like [[milk]], and dark leafy greens such as [[spinach]].  The [[bone marrow]] in the middle of the bigger bones makes our [[red blood cell]]s.

== Structure ==
=== Bone marrow ===
Long bones are hollow, with a central core which is not strong like the rest of the bone. It contains the [[bone marrow]], one of the most important [[tissues]] in the vertebrate body. It produces [[blood cells]] for the blood system, and [[lymphocytes]] for the [[immune system]]. {{-}}
[[File:Illu compact spongy bone.jpg|500px|center|thumb|Diagram of a typical long bone: shows compact (cortical) and cancellous (spongy) bone]]

=== Osteons ===
[[File:Transverse section of bone en.svg|thumb|right|300px|microscopic bone structure]]

Osteons are the small units of which the hardest parts of human bones are made. They are roughly cylindrical, and about 0.2mm wide and a few millimeters long. They are found in the bone in most [[mammals]], and many [[reptiles]], [[birds]] and [[amphibians]].<ref>Martiniaková, Monika 2003. Differences among species in microstructure of mammalian skeleton. Dissertation, Nitra</ref> Inside the osteons are bone cells called [[osteocyte]]s, each living in its own small space. Osteocytes make contact with each other by [[cytoplasmic]] processes through a network of tiny canals. This allows the exchange of nutrients and metabolic waste.  [[Collagen]] fibers in each ring of cells ('lamellae') give them structure.<ref>Cooper, Reginald R.; Milgram, James W.; and Robinson, Robert A. 1966. Morphology of the osteon: an electron microscopic study. ''Journal of Bone and Joint Surgery'', '''48''': 1239-1271.</ref>

Osteons have a hole down the middle, called the haversian canal. This canal contains the bone's [[blood]] supply. It also contains [[capillaries]], and [[nerve fibres]].<ref>{{Cite web|url = http://medical-dictionary.thefreedictionary.com/haversian|title = Haversian|first =|last =|website = The Free Dictionary|publisher =|accessdate = 2016-03-10}}</ref>

The details of osteon structure varies between bones and parts of bones, from species to species,  between sexes, and by age and environmental factors.<ref>Klevezal G. 1996. ''Recording structures of mammals''.</ref><ref>Paget's disease: http://www.pathology.vcu.edu/education/musculo/lab2g.htm{{Dead link|date=January 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

== References ==
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[[Category:Basic English 850 words]]
[[Category:Bones| ]]
[[Category:Natural materials]]