Vitals parts of worker kept nervously alert (9)
I believe the answer is:
heartland
'vitals parts' is the definition.
'heartland' can be an answer for 'parts' (thesaurus). I am unsure of the 'vitals' bit.
'worker kept nervously alert' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'kept' means one lot of letters goes inside another.
'nervously' indicates an anagram.
'alert' with letters rearranged gives 'eartl'.
'hand' placed around 'eartl' is 'HEARTLAND'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for heartland that I've seen before include "Vitally important area" , "Central part of a country or area" , "Central region of a country" , "central zone" , "A most vital area" .)