Explain the main features of Selye's General Adaptation Syndrome?

In 1936 Hans Selye developed his theory of the General Adaptation Syndrome (GAS), which is a stress model that explains the body's physiological response to stress. These stress responses are divided into three stages: alarm, resistance and exhaustion. During the initial phase of the body's reaction to stress (alarm), the fight or flight mechanism is triggered in order to prepare the body for physical activity, thus allowing it to defend itself against a potential threat. The second stage of the body's stress response is characterised by a lowering level of stress due to the body's allocation of energy to damaged tissue. As a result, the stress response during this phase is minimised. Finally, in the exhaustion phase, the body can no longer fight against the stressors because of the depletion of energy resources. Thus, if the cause of stress is not resolved immediately, health issues may occur. Selye's theory of GAS represents a biological explanation of how the body responds and adapts to the presence of stressors.