Vital supplier devised a rota (5)
I believe the answer is:
aorta
'vital supplier' is the definition.
(vital artery)
'devised a rota' is the wordplay.
'devised' indicates anagramming the letters.
'a'+'rota'='arota'
'arota' anagrammed gives 'AORTA'.
(Other definitions for aorta that I've seen before include "Trunk artery from the heart" , "Vital blood vessel" , "Blood carrier" , "Major artery of the body" , "blood flows from it" .)