What part of the autonomic nervous system regulates the 'fight-or-flight' response?

Sympathetic : The system responsible for Adrenalin production, the sympathetic nervous system.

Various: Your autonomic nervous system (ANS) controls virtually all the organs and systems in your body. If your sympathetic nervous system(sns) hyper - you could have cold hands, palpitations, sweating, htn, dry mouth, constipation, dry eyes, dry mouth. This is known as the "fight or flight" response and is the result of adrenaline and other stimulatory factors associated with your sns.