Which hormone is primarily involved in the body's fight-or-flight response?

The hormone primarily involved in the body's fight-or-flight response is epinephrine. When faced with a stressful situation, the body activates its sympathetic nervous system, leading to the release of epinephrine from the adrenal medulla. This hormone serves to prepare the body for immediate physical action by increasing heart rate, dilating airways, and enhancing blood flow to vital organs and muscles, alongside decreasing blood flow to non-essential systems.

Epinephrine's rapid action is crucial for survival, allowing an organism to react swiftly to threats. It initiates a cascade of physiological responses that enhance alertness and physical performance during stressful situations. Unlike other hormones that have more long-term regulatory roles or specific functions, such as cortisol (which is involved in stress response but over a longer duration), testosterone (mostly related to reproductive functions), and insulin (which regulates glucose metabolism), epinephrine is directly linked to acute stress response, making it the key player in the fight-or-flight reaction.