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 wordplay.
'and' means one lot of letters go next to another.
'to get damaged' indicates an anagram.
'vitalprone' with letters rearranged gives 'PORTAL VEIN'.
(Another definition for portal vein that I've seen is "What supplies liver".)