Hans Selye's GAS Model explains the influence of stress on the body.

• From his studies, he found that there was a similar pattern of bodily responses in animals to a variety of stressors.

• According to Hans Selye, stress refer to non-specific bodily reactions. He believed that stresses may be many but responses are only physiological reactions. Selye is known as 'father of modern stress researches'. He did many experiments on animals in extreme climatic conditions as well as he observed chronic patients and concluded that reaction of stress is the same.

• On the basis of his experimental conclusions, he gave a pattern of stress reactions. He called this pattern the General Adaptation Syndrome and it involves three stages:

1. Alarm Reaction: The presence of a harmful stimulus or stressor leads to activation of the adrenal-pituitary-cortex system.

This triggers the release of hormones which produces the stress response and prepares the individual for fight or flight.

2. Resistance: If stress is prolonged, the parasympathetic nervous system calls for more cautious use of the body's resources.

During this stage, an individual makes an effort to cope with the threat.

3. Exhaustion: Continued exposure to the same stressor or additional stressors drains the body of its resources and leads to burn out.

The physiological systems involved in the first two stages become ineffective and susceptibility to stress-related diseases like high blood-pressure increases. This model is widely criticized because it focuses only on physiological aspects of stress and ignores the psychological dimension of stress.