What triggers the fight or flight response in the body?

The fight or flight response, a crucial physiological reaction to perceived threats, is primarily triggered by the release of catecholamines from the adrenal glands. When a person encounters a stressful situation, the body's sympathetic nervous system is activated. This leads to the adrenal medulla releasing catecholamines, mainly adrenaline (epinephrine) and noradrenaline (norepinephrine). These hormones prepare the body to respond to danger by increasing heart rate, dilating the airways, boosting blood flow to muscles, and mobilizing energy stores, thus enabling a rapid response to threats.

The other choices do not centrally trigger the fight or flight response. While a reduction of insulin levels can influence energy availability, it is more a part of the metabolic adjustments occurring after the initial stress response. Increased glucose uptake is not a direct trigger; rather, the body aims to mobilize glucose for quick energy during the response. Stimulation of the vagus nerve generally promotes rest and digestion, counteracting the fight or flight response rather than initiating it.