The primary function of adrenaline in the body is to prepare for 'fight or flight' responses during stress. Secreted by the adrenal glands, adrenaline increases heart rate, elevates blood pressure, and enhances energy production by mobilizing glucose and fatty acids. These physiological changes enable rapid responses to threats, enhancing physical performance and focus. Adrenaline also influences various systems, including the respiratory and immune systems, contributing to an individual's overall readiness to cope with emergencies.