An immediate response to any stimulus that potentially threatens the wellbeing of an organism. It involves the release of adrenaline and noradrenaline from the adrenal glands, triggered by increased sympathetic nervous activity. These hormones enhance the effects of the sympathetic nervous system (e.g. by increasing heart and breathing rates) and promote glycogen breakdown, which supplies large amounts of glucose for increased respiration and energy release. They also promote the release of glucose by liver cells and of fatty acids from fat cells. Compare resistance response.