General adaptation syndrome is the set of changes in various organ systems of the body, especially the pituitary-endocrine system, in response to a wide range of strong external stimuli, both physiological and psychological. It is described as having three stages: alarm reaction, where the body detects the external stimulus; adaptation, where the body engages defensive countermeasures against the stressor; and exhaustion, where the body begins to run out of defenses. (Gene Ontology, GO_0051866)
