In freudian psychoanalysis, ego along with id and superego, are the three components of the psychic apparatus. It spans the conscious, preconscious, and unconscious; is the structure within the personality functioning in an executive capacity to mediate conflict between the id and the outside world, as part of the progression from the dominance of the pleasure principle to that of the reality principle and subsequently mediates the conflict between the id and superego and itself. It perceives from moment to moment external reality, needs of the self (both physical and psychological), integrates the perceptions and uses of logical, abstract, secondary process thinking, and the mechanisms of defense available to it to formulate a response.
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Examples: glitazone, GI cocktail, etc.