Fight or flight response

The fight or flight response - a sequence of activity within the body that is triggered when the body prepares itself for defending or attacking or running away to safety. 

This activity involves changes to the nervous system and the secretionof hormones that are necessary to sustain arousal.

During a stressful event the endoctrine and the autonomic nervous system work in parellel with each other. 

When a stressor is percieved the first thing that happens is the hypothalumus triggers activity in the sympathetic part of the autonomic nervous system.

The ANS changes from the resting state ( parasympathetic state ) to the physiologically aroused state ( sympathetic state ).

The stress hormone adrenaline is released from the adrenal medulla into the bloodstream. 

Adrenaline triggers physiological processes within the body. All of this happens as soon as a threat is detected. 

The physiologically changes associated with the sympthectic state are:                  increased heart rate, increased breathing rate, dilated pupils, inhibits digestion, inhibits saliva production and contracts rectum.

Finally, once the threat has passed, the parasympathetic part of the ANS works in opposition to the sympathetic nervous system. 

When in the parasympathetic state our heart rate decreases, breathing rate decreases, constricts pupils, stimulates digestion, stimulates saliva production and relaxes rectum.