We've installed channels of circulation inside (5)
I believe the answer is:
veins
'channels of circulation inside' is the definition.
The answer and definition can be both body parts as well as being plural nouns.
Perhaps they are linked in a way I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for veins that I've seen before include "Circulation aids" , "Characteristic styles" , "Layers of ore" , "Blood vessels" .)