Final answer:
Adrenaline, also known as epinephrine, is the hormone responsible for triggering the "fight or flight" response during stressful situations.
Step-by-step explanation:
The hormone that elicits the "fight or flight" response is adrenaline (or epinephrine). This is a non-steroid catecholamine hormone produced by the medulla of the adrenal glands. The adrenal medulla releases adrenaline during stress-induced disruptions of homeostasis. This prepares the body to either fight for survival or flee from danger by increasing energy levels through raised blood glucose levels, among other effects.