Rota devised by a vital supplier (5)
I believe the answer is:
aorta
'vital supplier' is the definition.
(vital artery)
'rota devised by a' is the wordplay.
'devised' indicates an anagram.
'by' says to put letters next to each other.
'rota' with letters rearranged gives 'aort'.
'aort'+'a'='AORTA'
(Other definitions for aorta that I've seen before include "Great artery in body" , "Trunk route" , "claret supplier" , "Bloody channel" , "Main artery of body" .)