Adrenaline is a hormone produced by the adrenal glands during high stress or exciting situations. This powerful hormone is part of the human body's acute stress response system, also called the "fight or flight" response. It works by stimulating the heart rate, contracting blood vessels, and dilating air passages, all of which work to increase blood flow to the muscles and oxygen to the lungs. Additionally, it is used as a medical treatment for some potentially life-threatening conditions including anaphylactic shock. In the US, the medical community largely refers to this hormone as epinephrine, although the two terms may be used interchangeably.
The Adrenal Glands
The adrenal glands are found directly above the kidneys in the human body, and are roughly 3 inches (7.62 cm) in length. Adrenaline is one of several hormones produced by these glands. Along with norepinephrine and dopamine, it is a catecholamine, which is a group of hormones released in response to stress. These three hormones react with various body tissues, preparing the body to react physically to the stress causing situation.
The Fight or Flight Response
The term "fight or flight" is often used to characterize the body's reaction to very stressful situations. It is an evolutionary adaptation that allows the body to react to danger quickly. Dilated air passages, for example, allow the body to get more oxygen into the lungs quickly, increasing physical performance for short bursts of time. The blood vessels contract in most of the body, which redirects the blood toward the heart, lungs, and major muscle groups to help fuel the reaction.
When a person encounters a potentially dangerous situation, the hypothalamus in the brain signals the adrenal glands to release adrenaline and other hormones directly into the bloodstream. The body's systems react to these hormones within seconds, giving the person a nearly instant physical boost. Strength and speed both increase, while the body's ability to feel pain decreases. This hormonal surge is often referred to as an "adrenaline rush."
In addition to a noticeable increase in strength and performance, this hormone typically causes heightened awareness and increased respiration. The person may also feel lightheaded, dizzy, and experience changes in vision. These effects can last up to an hour, depending on the situation.
When there is stress but no actual danger, a person can be left feeling restless and irritable. This is partly because adrenaline causes the body to release glucose, raising blood sugar, and giving the body energy that has no outlet. Many people find it beneficial to "work off" the adrenaline rush after a particularly stressful situation. In the past, people handled this naturally through fighting or other physical exertion, but in the modern world, high-stress situations often arise that involve little physical activity. Exercise can use up this extra energy.
Though adrenaline can play a key role in the body's survival, it can also cause detrimental effects over time. Prolonged and heightened levels of the hormone can put enormous pressure on the heart muscle and can, in some cases, cause heart failure. Additionally, it may cause the hippocampus to shrink. High levels of adrenaline in the blood can lead to insomnia and jittery nerves, and are often an indicator of chronic stress.
First synthesized in 1904, adrenaline is a common treatment for anaphylaxis, also known as anaphylactic shock. It can be quickly administered to people showing signs of severe allergic reactions, and some people with known severe allergies carry epinephrine auto-injectors in case of an emergency. For these individuals, dosage should be assigned by a licensed medical professional in advance, and instructions should be given on how and where it should be administered.
Adrenaline is also one of the main drugs used to treat low cardiac output — the amount of blood the heart pumps — and cardiac arrest. It can stimulate the muscle and increases the person's heart rate. In addition, by concentrating blood in the vital organs, including the heart, lungs, and brain, it helps increase the chances that the person will recover more fully.