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==Physiologic significance==
 
==Physiologic significance==
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It is traditionally believed that the arrangement of the brain's arteries into the Circle of Willis creates redundancies in the cerebral circulation. If any one of the arteries in the circle become blocked or narrowed ([[stenosis|stenosed]]) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other [[blood vessel]]s can usually maintain cerebral perfusion.
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The arrangement of the brain's arteries into the Circle of Willis creates redundancies in the cerebral circulation. If any one of the arteries in the circle become blocked or narrowed ([[stenosis|stenosed]]) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other [[blood vessel]]s can usually maintain cerebral perfusion.
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This traditional view is, however, not in accordance with principles of [[natural selection]]. The circle of Willis is also present in many non-human species ([[reptiles]], [[birds]] and [[mammals]]), and arterial narrowing is usually associated with aging and the human lifestyle. Therefore, evolutionarily correct and more generally applicable explanations of its functions have been suggested, such as dampening of [[Blood pressure|pulse pressure waves]] within the brain<ref>Vrselja Z, Brkic H, Mrdenovic S, Radic R, Curic G. (2014). Function of Circle of Willis. ''Journal of Cerebral Blood Flow & Metabolism'' 34(4), pp. 578-584. DOI: [https://journals.sagepub.com/doi/full/10.1038/jcbfm.2014.7 10.1038/jcbfm.2014.7]</ref> and involvement in [[forebrain]] sensing of water loss by [[Circumventricular organs|sensory circumventricular organs]].<ref>Fenrich M, Habjanovic K, Kajan J, Heffer M. (2020). The circle of Willis revisited: Forebrain dehydration sensing facilitated by the anterior communicating artery. ''BioEssays'', e2000115. DOI: [https://www.researchgate.net/profile/Matija_Fenrich/publication/345940509_The_circle_of_Willis_revisited_Forebrain_dehydration_sensing_facilitated_by_the_anterior_communicating_artery/links/5fb2679b299bf10c36837722/The-circle-of-Willis-revisited-Forebrain-dehydration-sensing-facilitated-by-the-anterior-communicating-artery.pdf 10.1002/bies.202000115]</ref>
 
   
 
==Anatomic variation==
 
==Anatomic variation==

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