==Key Stage 3==
===Meaning===
A An [[vein]] is a [[blood vessel]] which carries [[blood]] to the [[heart]].
===Key Stage 4===
===Meaning===
A An [[vein]] is a [[blood vessel]] which carries low [[pressure]] [[blood]] to the [[heart]]. ===Adaptations of Arteries===: [[Vein]]s have a thin layer of [[muscle]] because the [[blood]] is a low [[pressure]].: [[Vein]]s have few layers of elastic [[tissue]] as the [[blood]] is a low [[pressure]].: [[Vein]]s have [[valve]]s in them to stop the [[blood]] flowing in the wrong direction because it is such a low [[pressure]].: [[Vein]]s often pass between [[muscle]]s which work with the [[valve]]s by contracting to force the [[blood]] through the [[vein]]. {| class="wikitable"|-|[[File:Vein.png|center|300px]]|-| style="height:20px; width:200px; text-align:center;" |A [[diagram]] of an [[vein]].|} ===About Arteries===: Most, but not all, '''arteries''' carry [[oxygenated]] [[blood]].