Adrenaline, chemically known as epinephrine, is a catecholamine hormone and neurotransmitter critical to the endocrine system. It plays a vital role in the body's acute stress response, commonly referred to as the "fight-or-flight" mechanism. Its release rapidly signals immediate physiological adjustments designed to maximize energy availability for potential physical exertion. Key effects include increasing cardiac output and heart rate, elevating blood pressure, and causing the peripheral vasoconstriction of non-essential areas while promoting increased blood flow to major muscle groups. Furthermore, adrenaline stimulates the liver to undergo glycogenolysis, rapidly mobilizing glucose into the bloodstream to ensure immediate energy supplies for critical metabolic processes.