Which branch of the autonomic nervous system begins to energize the body for the "fight or flight" syndrome?

The branch of the autonomic nervous system for the "fight or flight" response is the sympathetic nervous system. The main function of the sympathetic nervous system in the "fight or flight" response is that it stimulates the adrenal medulla to produce cathecolamines such as epinephrine and norepinephrine. The sympathetic nervous system also acts to increase heart rate and respiratory rate to prepare the body to a stressful situation. The sympathetic nervous system also inhibits the activity of the gastrointestinal and urinary tracts.