adrenaline

n. A hormone (C₉H₁₃NO₃) and neurotransmitter created in the adrenal glands which acts primarily as an arousal agent. Adrenaline causes an increase in heart rate and heart stroke volume, dilates the pupils, increases blood sugar levels, reduces blood flow to the skin and digestive tract, increases blood flow to the muscles, and suppresses immune function. Adrenaline is used to stimulate the heart in cases of cardiac arrest and sometimes in cardiac arrhythmias. Adrenaline is one of the main neurotransmitters in the fight-or-flight response and in activation of the reticular activating system (RAS). Its action is mimicked by amphetamines, caffeine, and Ritalin. ► See also EPINEPHRINE