General Adaptation Syndrome ( GAS )

When Hans Selye was conducting research on rats by injecting them with extracts of various glands of the body, he noticed that the rats were all displaying the same group of symptoms. At first he believed that he had discovered a new hormone; however, after several years of further testing by injecting the rats with other substances, such as formaldehyde revealed the same results. Even exposure to cold, cutting their spinal cords and forced exercise produced the same effects. The effects occurred in a predictable sequence that is now known as the General Adaptation Syndrome (GAS).

Stage 1 : Alarm

Selye called the first stage of the General Adaptation Syndrome the General Alarm Reaction. This reaction is the result of the biological processes that were described in the section on The Body's Response to stress: Signals are sent to the sympathetic division of the ANS, which increases heart rate, dilates bronchi, inhibits digestion, converts glycogen to glucose etc; meanwhile the hypothalamus also releases CRF, which in turn prompts the release of ACTH from the pituitary which stimulates the secretion of cortisol from the adrenal-cortex.

Stage 2 : Resistance

If the stressor is not removed the body attempts to adapt to the stress and in the second stage, resistance, it is largely successful; nevertheless, adrenaline and cortisol levels remain high. The consequence of this is that although the body is able to cope, its resources are depleted. If the stress continues for longer the third stage of the syndrome is reached.

Stage 3 : Exhaustion

Resistance to stress can only be maintained for a limited amount of time. As the body's resources become depleted, the immune system is weakened and health problems develop.