How Does Adrenaline Work?

The Science of Adrenaline

The biological events that cause the adrenal glands to release adrenaline set in motion a wide array of changes in bodily functions.

The adrenal glands are important endocrine glands that are found adjacent to the top of each of the kidneys. One of the most critical hormones produced by the adrenal gland, it is also named for that gland. Adrenaline, also known as epinephrine (often abbreviated as “epi” in the hospital), is what is known as a catecholamine and is a key component in the stimulation involved in the “fight or flight” response. It is normally produced by the specialized adrenal chromaffin cells in the adrenal medulla (the central portion of the adrenal gland) in response to various signals that stimulate the gland.

Adrenaline can be Useful

Although adrenaline has been much maligned for its detrimental effects within the human body, it still has its uses. It for example requires regular exercise, which is beneficial in maintaining a healthy body. It can also be useful when taking breaks, providing a pleasurable rush when taking part in extreme sports or recreation. Such an adrenaline rush provides a good way to work away the stress experienced during normal working hours. It is important to be aware of the functions of adrenaline in the body. In this way, both a healthy body and mind can be maintained.

Adrenaline, like most hormones, is able to bind to specific “receptor” proteins on cells, activating them and causing its effects. When it is released into the circulation, adrenaline binds to and activates what is known as adrenoreceptors on target cells. These are also commonly referred to as adrenergic receptors, and there are two general classes, alpha, and beta (with each having several subclasses). The commonly used medications known as “beta-blockers”, work by selectively interfering with the activation of beta-adrenoreceptors. Adrenaline, on the other hand, is a non-selective activator of all types of adrenoreceptors.

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History and Effects of Adrenaline

The name epinephrine was coined by John Jacob Abel in 1898. It is a combination of the Latin and Greek terms meaning above (epi-) and kidney (nephros), referring to the location of the adrenal gland in the body. Abel was also the one who first isolated the hormone from the gland.

The effects of adrenaline are designed to help the body cope with physical exhilaration. This was particularly useful in ancient times when threats were most often physical. These threats required what is known as the “fight or flight” response. Adrenaline would then help the body prepare to either defend itself or to run from danger.

  • Specifically, the effects of adrenaline include:
  • Dilated blood vessels;
  • Dilated air passages;
  • Increased heart rate;
  • Increased blood pressure

Adrenaline Today

Together with a faster heart rate, the dilated blood vessels helped to channel an increase of blood flow to the major muscle groups. This would provide a spurt of physical energy to cope with the physical requirements of the situation. The dilated air passages also allowed more oxygen to enter the body so it could function better and more efficiently. This is why deep breathing is such a good way to cope with stress.

An interesting fact is that not only adrenaline is released in response to stressful situations. Norepinephrine (also known as noradrenaline) is also released. When the adrenal glands are active, roughly 20% of the hormone released consists of Norepinephrine. In addition, cortisol is also released to help strengthen the body for a physical response to threats.

The language surrounding the hormone is also interesting. The general American public tends to refer to the hormone-like adrenaline. The medical community however prefers the term epinephrine. The reason for this was that the term “adrenalin” was trademarked by a pharmaceutical company. The distinction is only made in the official medical language, however. The popular term, adrenaline, is used frequently enough to preclude confusion.

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Molecules similar to Adrenaline

Understanding how adrenaline works might be easier to grasp if one considers the drugs that are very similar in structure to adrenaline and mimic its effects, for many of them at a grotesquely overactivated scale. The amphetamines and most of their derivatives are chemically related to the structure of adrenaline. This includes Benzedrine, Dexedrine, methamphetamine, and MDMA, also known as Ecstasy.

What Effects Does Adrenaline Have?

Adrenaline can act on many cells in the body, and it also can be used as a neurotransmitter when it is synthesized by specific classes of nerve cells in the nervous system. Most commonly, however, it is the actions outside of nerves that generate the characteristic response of the body to adrenaline.

Acting on muscle and liver cells, adrenaline causes the cells to break down the complex storage carbohydrate glycogen and release extra glucose into the bloodstream (a much more readily usable source of energy). Acting on cells in the digestive tract, adrenaline causes a reduction in digestive secretions and acts on the blood vessels to shunt blood away from the gut and towards the brain, heart, lungs, and muscles. Adrenaline also has important direct effects on the heart and lungs, stimulating the heart rate and the overall force of contraction of the heart muscle and dilating (widening) the airways in the lungs so that oxygen absorption can be enhanced.

For some of the very effects described above, adrenaline (or compounds related to it structurally) is used quite frequently in important medical situations. For people with a history of severe allergic reactions, carrying an Epi-Pen loaded with epinephrine (adrenaline) can be critical. Some respiratory inhalers for use with asthma are loaded with a compound related to adrenaline. And in the case of some cardiac rhythm disturbances, administration of adrenaline can be an absolute life-saver.

Knowing the effects of adrenaline makes it easier to understand how the fight or flight response comes as advertised.

Reference: Arthur C. Guyton, MD and John E. Hall, PhD; Textbook of Medical Physiology, 11th Edition; Elsevier; ISBN:978-0-7216-0240-0

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