What is Artery?
An '''artery''' is a [[blood vessel]] that carries [[blood]] away from the [[heart]] to other parts of the body. Almost all arteries carry blood with a lot of [[oxygen]] in it. The only arteries that do not carry oxygen-rich blood are the [[pulmonary artery]], and (in a [[fetus]]) the [[Umbilical cord|umbilical]] artery.<ref name=brit>{{cite web |url=http://www.britannica.com/science/artery |title=Artery: Anatomy |author=<!--Staff writer(s); no by-line.--> |date=January 14, 2016 |website=Britannica.com |publisher=Encyclopædia Britannica |access-date=January 29, 2016 }}</ref> Every artery has three layers. The outer layer is a thick covering made of stretchy [[tissue]]. The middle layer is made of [[muscle]], so the artery can [[Vasodilation|get wider]] or [[Vasoconstriction|get smaller]] when the body needs it to. The inner lining is made of the same [[cell]]s that line the heart.<ref name=cs>{{cite web |url=http://www.cedars-sinai.edu/Patients/Programs-and-Services/Heart-Institute/Centers-and-Programs/Aortic-Program/Anatomy-of-the-Aorta-and-Heart.aspx |title=Anatomy of the Aorta and Heart |author=<!--Staff writer(s); no by-line.--> |date=2016 |website=Cedars-Sinai Heart Institute – Aortic Program |publisher=Cedars-Sinai |access-date=January 29, 2016 |archive-date=February 11, 2016 |archive-url=https://web.archive.org/web/20160211100144/http://www.cedars-sinai.edu/Patients/Programs-and-Services/Heart-Institute/Centers-and-Programs/Aortic-Program/Anatomy-of-the-Aorta-and-Heart.aspx |url-status=dead }}</ref> Arteries are deep under the [[skin]]. They do not have valves to prevent blood from flowing backwards. Instead, every time the heart beats, the arteries stretch out so the blood has room to go through. Once the walls have completely stretched out, the muscles in the arteries make them shrink back to their normal size. This pushes the blood through.<ref name=brit/> Arteries split down into small vessels called ''arterioles''. == Important arteries == === The aorta === [[File:Arterial System en.svg|t