Organs of state constrained by egos periodically (6)
I believe the answer is:
glands
'organs' is the definition.
(gland is a kind of organ)
'state constrained by egos periodically' is the wordplay.
'state' becomes 'land' (synonyms).
'constrained by' means one lot of letters goes inside another.
'periodically' indicates alternate letters (letters must be selected 'every so often').
The alternate letters of 'egos' are 'gs'.
'land' put within 'gs' is 'GLANDS'.
'of' acts as a link.
(Other definitions for glands that I've seen before include "Body organs that release secretions" , "Various body organs that secrete substances" , "These body parts secrete substances" , "Organs that separates substances in the blood" , "Lymph and adrenal, say" .)