General Adaptation Syndrome
The father of stress research is Hans Selye. When trying to discover a new sex hormone, he injected rats with ovarian hormone extract. What resulted was much different than expected. When dissecting the deceased rats, he found their adrenal cortex to be enlarged, their thymus gland to be shrunken, and ulcers to be bleeding.
No matter what fluids he injected in the rats, the response was the same and concluded these effects were not due to a new hormone. He soon connected the response possibly to be a general bodily response to damage of any kind so he experimented by studying animals' responses to various stressors, and he found that this response was universal and named it the general adaptation syndrome (GAS), which he saw as having three phases.
The Three Phases:
​1. Alarm: stressor begins and the body mobilizes its resources and prepares itself for phase 2.
2. Resistance: the alarm reaction remains high and the body copes with the stressor (fights or flights), and, if the stressor continues, the body moves to phase 3.
3. Exhaustion: the body's resources deplete, and the body is more vulnerable to sickness and, in some cases, collapse and death.