"the phase of the gas occurs when an organism initially encounters a stressor."

The __Alarm___ phase of the GAS occurs when an organism initially encounters a stressor.

Explanation:

In body there is a process consists of three stages which describe the on going physiological changes in the body under stress condition. This process is called GAS (General Adaptation Syndrome).

Among three stages of GAS there is a Alarm Phase. In Alarm phase hypothalamus receives a dis-stress stimuli and release glucocorticoids. This hormone initiate the release of two stress hormones called cortisol and Adrenalin. Both hormones increases the heart rate and boost the person's energy which results in increased blood pressure.

Furthermore, alarm phase prepare response of person according to stressor they are encountering with. This is also called as fight and flight repose.

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