Circulation of family confused master (11)
'circulation' is the definition.
'family confused master' is the wordplay.
'family' becomes 'blood' (I've seen this in other clues).
'confused' indicates an anagram.
'master' with letters rearranged gives 'stream'.
'of' acts as a link.
(Other definitions for bloodstream that I've seen before include "It circulates in vessels", "current in vessels", "Vital channel", "vital passage", "something essential to human life".)