Which hormone triggers the fight-or-flight response by increasing heart rate during a crisis?

• A. Norepinephrine
• B. Epinephrine
• C. Glucagon
• D. Insulin

Answer: (B)

In a crisis, the body’s sympathetic fight-or-flight pathway triggers the adrenal medulla to release epinephrine (adrenaline) into the bloodstream. Epinephrine travels through the blood and binds to beta-adrenergic receptors on the heart, increasing both the rate and force of heart contractions. This quick boost in cardiac output delivers more oxygen and glucose to muscles, preparing the body to either fight or flee. Norepinephrine also supports sympathetic signaling and can affect heart rate, but epinephrine is the primary circulating hormone that drives the systemic fight-or-flight response. Glucagon raises blood sugar in a slower, metabolic way, and insulin lowers blood glucose and doesn’t acutely raise heart rate, so they’re not the immediate drivers of the crisis-induced heart-rate increase.