Retired nurse I retrained to secure body parts (8)
I believe the answer is:
arteries
'body parts' is the definition.
(artery is a kind of body part)
'retired nurse i retrained to secure' is the wordplay.
'retired' is a reversal indicator.
'to secure' indicates a hidden word (I've seen 'securing' mean this).
'seiretra' is hidden in the letters of 'nurse i retrained'.
'seiretra' back-to-front is 'ARTERIES'.
(Other definitions for arteries that I've seen before include "Blood vessels - major roads" , "Vessels that carry blood from the heart to the body" , "Major thoroughfares for important traffic" , "Blood vessels leading from the heart" .)