Adrenaline, a natural stimulant created in the kidney's adrenal gland, travels through the bloodstream and controls functions of the autonomous nervous system, including the secretion of saliva and sweat, heart rate and pupil dilation. The substance also plays a key role in the human flight-or-flight response.
According to News Medical the body releases adrenaline, also known as epinephrine, when the brain perceives a threat. Once adrenaline enters the bloodstream, it sparks a series of responses, all geared toward responding to the perceived threat. These responses include a rush of energy to allow muscles to engage quickly and powerfully, and increase in the blood's ability to clot in the event of a physical injury and increased hearing sensitivity.
On its You & Your Hormones website, the Society for Endocrinology reports that adrenaline's provocation of the flight-or-flight response is essentially a means of preparing the body and brain for abrupt and vigorous action and therefore, in a normal, healthy person, only occurs during times of acute stress. The production, release and effects of adrenaline occur relatively quickly, usually within three minutes. Once the frightening situation ends, adrenal gland nerve impulses slow, signaling the body to stop generating adrenaline.