Hoop-la's main component of blood (6)
I believe the answer is:
plasma
'blood' is the definition.
(thesaurus)
'hoop-la's main component' is the wordplay.
'component' indicates the answer is hidden within the clue (I've seen 'components' mean this (some components of the word make the answer)).
'PLASMA' can be found hidden inside 'hoop las main'.
'of' is the link.
(Other definitions for plasma that I've seen before include "TV screen type" , "part of donor's contribution?" , "Liquid part of blood" , "A psalm (anag.)" , "Hot ionised gas" .)