You have two parts to the autonomic nervous system. You have the sympathetic and parasympathetic response. The adrenalin rush is part of the sympathetic response. Imagine you are walking in the woods and out of no where a bear starts chasing you....your blood pressure goes up, your heart rate increases, your bronchioles dialate as do your pupils. This is the fight or flight. During this event your sdrenal glands are secreting adreneline very quickly. You climb a tree and the bear can't get you. You wait 30 min and the is no sign of the bear. Now your heart rate will decrease, your blood pressure will come down and yoour bronchioles and pupils will constrict. This is the parasympathetic or feed and breed response.
