The document summarizes Selye's General Adaptation Syndrome (GAS) model of the body's response to stress. The GAS consists of three stages: alarm reaction, resistance, and exhaustion. In the alarm reaction stage, the body prepares to respond to stress. In the resistance stage, the body continues to defend against stress. If stress is prolonged and unmanageable, it can lead to tissue damage, disease, and even death in the exhaustion stage. The GAS was the first systematic model of stress response but has been criticized for not accounting for psychological factors and individual differences.