Vital artery (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">vital artery</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for aorta that I've seen before include "Large trunk artery" , "Heart's great artery" , "Main route from the heart" , "A rota (anag)" , "blood flows from it" .)