Utente:BlackPanther2013/Sandbox: differenze tra le versioni
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[[File:Flickr - Rainbirder - Reticulated Giraffe drinking.jpg|thumb|left|Giraffa che beve. Una rete mirabile impedisce un'afflusso di sangue al cervello quando il collo viene abbassato.]]
In mammals, the left [[recurrent laryngeal nerve]] is longer than the right; in the giraffe it is over {{convert|30|cm|in|abbr=on}} longer. These nerves are longer in the giraffe than in any other living animal;<ref name="Wedel">{{Cite journal|author=Wedel, M. J.|year=2012|title=A monument of inefficiency: the presumed course of the recurrent laryngeal nerve in sauropod dinosaurs|journal=Acta Palaeontologica Polonica|volume=57|issue=2|pages=251–56|doi=10.4202/app.2011.0019|url=http://www.app.pan.pl/archive/published/app57/app20110019.pdf}}</ref> the left nerve is over {{convert|2|m|abbr=on}} long.<ref>{{cite book|author=Harrison, D. F. N.|year=1995|title=The Anatomy and Physiology of the Mammalian Larynx|publisher=Cambridge University Press|page=165|isbn=0-521-45321-6}}</ref> Each nerve cell in this path begins in the [[brainstem]] and passes down the neck along the [[vagus nerve]], then branches off into the recurrent laryngeal nerve which passes back up the neck to the larynx. Thus, these nerve cells have a length of nearly {{convert|5|m|abbr=on}} in the largest giraffes.<ref name="Wedel"/> The structure of a giraffe's brain resembles that of domestic cattle.<ref name=Williams/>{{rp|31}} The shape of the skeleton gives the giraffe a small lung volume relative to its mass.<ref name=SkinnerJD2011>{{Cite journal|author=Skinner, J. D.; Mitchell, G.|year= 2011|title= Lung volumes in giraffes, ''Giraffa camelopardalis''|journal= Comparative Biochemistry and Physiology – Part A: Molecular & Integrative Physiology|volume= 158|issue= 1|pages= 72–78|doi= 10.1016/j.cbpa.2010.09.003|url= http://137.215.9.22/bitstream/handle/2263/16472/Mitchell_Lung(2011).PDF?sequence=1}}</ref> Its long neck gives it a large amount of [[Dead space (physiology)|dead space]], in spite of its narrow windpipe. These factors increase the resistance to airflow. Nevertheless, the animal can still supply enough oxygen to its tissues.<ref name=SkinnerJD2011/>
[[File:Giraffe-Drinking-Nairobi.JPG|thumb|right|
The [[circulatory system]] of the giraffe has several adaptations for its great height. Its heart, which can weigh more than {{convert|25|lb|kg|abbr=on|disp=flip}} and measures about {{convert|2|ft|cm|abbr=on|disp=flip|-1}} long, must generate approximately double the blood pressure required for a human to maintain blood flow to the brain. As such, the wall of the heart can be as thick as {{convert|7.5|cm|in|abbr=on}}.<ref name="Prothero 2003"/> Giraffes have unusually high heart rates for their size, at 150 beats per minute.<ref name=anatomy/>{{rp|76}} In the upper neck, a [[rete mirabile]] prevents excess blood flow to the brain when the giraffe lowers its head.<ref name= "MacDonald"/> The [[jugular vein]]s also contain several (most commonly seven) valves to prevent blood flowing back into the head from the [[inferior vena cava]] and [[right atrium]] while the head is lowered.<ref>{{cite journal|doi=10.3957/056.039.0210|author=Mitchell, G.; van Sittert, S. J.; Skinner, J. D.|title=The structure and function of giraffe jugular vein valves|journal= South African Journal of Wildlife Research|volume=39|issue=2|pages=175–80|url=http://137.215.9.22/bitstream/handle/2263/13994/Mitchell_Structure(2009).pdf?sequence=1 |year=2009}}</ref> Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). To solve this problem, the skin of the lower legs is thick and tight; preventing too much blood from pouring into them.<ref name= "MacDonald"/>
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