Blood vessel - vital and prone to get damaged (6,4)
I believe the answer is:
Here is my best explanation:
'blood vessel' is the definition.
(portal vein is a kind of blood vessel)
'vital and prone to get damaged' is the subsidiary indication.
'and' is a charade indicator (letters next to each other) (I've seen this in other clues).
'to get damaged' indicates anagramming the letters.
'vital' after 'prone' is 'pronevital'.
'pronevital' is an anagram of 'portalvein'.