Vessel heads off as our relatives turn away (5)
I believe the answer is:
aorta
'vessel' is the definition.
(blood vessel)
'heads off as our relatives turn away' is the wordplay.
'heads off' indicates taking the first letters (I've seen 'heading off' mean this).
'away' becomes 'A' (abbreviation as used in sports fixtures).
The initial letters of 'as our relatives turn' is 'aort'.
'aort'+'a'='AORTA'
(Other definitions for aorta that I've seen before include "main arterial route" , "Major blood vessel" , "Main human artery" , "A rota (anag)" , "Main arterial vessel, carrying blood to the heart" .)