Adrenaline, or epinephrine, is a hormone produced by the adrenal gland. Adrenaline increases heart rate, constricts blood vessels, dilates air passages and heightens physical performance; in other words, adrenaline improves the body’s reactivity, immediately priming it for “fight or flight”.

Like norepinephrine, with which it shares its origin and several actions, adrenaline is a “neurotransmitter” of the sympathetic nervous system. A violent and unexpected noise in the dark, the shout of a joking friend who suddenly appears out of nowhere or the scratching sound of chalk on the chalkboard are all examples of stressful events that instantly activate the sympathetic nervous system.

The heart immediately increases the force and rate of contraction, and the air passages, pupils and the blood vessels of the appendicular muscles and the coronary system all dilate. Simultaneously, the digestive processes slow down considerably while skin and peripheral blood vessels constrict and blood pressure rises – all in order to gear up the body for imminent physical activity.