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Adrenaline, Noradrenaline, and the Stress Response in Humans

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Facing a gigantic ocean wave would probably trigger adrenaline production in many people.

Facing a gigantic ocean wave would probably trigger adrenaline production in many people.

Vital Hormones From the Adrenal Glands

Adrenaline is a hormone made by the adrenal glands. It plays a vital role in helping our body deal with emergencies. The hormone is also known as epinephrine. Adrenaline, a related chemical called noradrenaline or norepinephrine, and the sympathetic nervous system are important components of the fight or flight response in humans, which is also known as the stress response. The response consists of a set of rapid body changes that help us to either face the emergency or escape from the situation.

Our adrenal glands have many functions. They are located at the back of our abdomen, one on top of each kidney. Each gland consists of two parts—the outer cortex and the inner medulla—and each part produces a different group of hormones. Adrenaline and noradrenaline are made by the adrenal medulla.

The right adrenal gland (identified from the owner's point of view) is triangular in shape. The left adrenal gland has a semilunar shape, as shown in the video screen above.

Hormones secreted by the adrenal glands

Hormones secreted by the adrenal glands

The Fight or Flight Response in Humans

The flight or flight response is activated when we face an emergency situation that may harm us or is life threatening. In this situation, the adrenal medulla secretes extra adrenaline and noradrenaline into the bloodstream. The hormones have important effects on the body. Many of these effects serve to increase the blood flow to the muscles and divert blood away from areas that are not so vital during the emergency.

Like all cells, muscle cells use oxygen to produce energy from digested food. They get the oxygen and the required nutrients from blood. During a potentially dangerous situation, a person's muscle cells need more of these substances than normal. The additional chemicals enable them to produce extra energy, which helps the person to deal with the situation by fighting it or fleeing it. The increased blood flow supplies the cells with the necessary chemicals.

Effects of Adrenaline (or Epinephrine)

EffectBenefit During an Emergency

Increases heart rate

Speeds up blood flow to skeletal muscles

Increases the force of the heartbeat

Increases amount of blood sent to skeletal muscles

Increases blood pressure

Increases amount of blood sent to skeletal muscles

Dilates (expands) blood vessels in the skeletal muscles

Enables muscles to receive more oxygen and nutrients

Constricts (narrows) blood vessels in the skin

Reduces blood flow to skin so that more is available for the skeletal muscles

Reduces blood flow to intestine

Allows more blood to flow to the skeletal muscles

Dilates bronchioles (air passages in the lung)

Allows more oxygen to enter the body

Increases breathing rate

Allows more oxygen to enter the body

Dilates the pupils

Allows more light to enter the eyes for a better view of the emergency

Raises blood glucose level by stimulating glycogen breakdown in the liver

Increases amount of glucose available for the muscles to use in energy production (since glycogen contains stored glucose)

Adrenaline and Noradrenaline Facts

About eighty percent of the hormone molecules released by the adrenal medulla are adrenaline molecules and about twenty percent are noradrenaline molecules. Adrenaline and noradrenaline have very similar molecular structures, but in one part of the molecule adrenaline has a hydrogen atom while noradrenaline has a methyl group (CH3). The two chemicals also have very similar functions when they are released from the adrenal glands. However, noradrenaline acts as a neurotransmitter as well as a hormone. A neurotransmitter is a chemical that controls the passage of nerve impulses from one neuron (nerve cell) to another or from a neuron to a muscle or a gland.

This is a synapse. Neurotransmitter molecules are being released from vesicles in the first neuron and traveling to receptors on the membrane of the second neuron.

This is a synapse. Neurotransmitter molecules are being released from vesicles in the first neuron and traveling to receptors on the membrane of the second neuron.

Actions of Hormones and Neurotransmitters


  • A hormone is a chemical that is made by a gland and then secreted into the bloodstream, which transports it around the body. Specific parts of the body respond to the presence of the hormone. These parts are known as the target organs (or the target cells) of the hormone.

Neurotransmitters in the Space Between Neurons

  • Neurons don't touch each other. There is a tiny gap between one neuron and the next. Neurotransmitters are chemicals that transmit the nerve impulse through this gap or that influence the transmission of the nerve impulse through the gap. The region where one neuron ends and another begins is called a synapse.

Neurotransmitters in the Space Between a Neuron and a Muscle or Gland

  • The word "synapse" also refers to the region where the end of a neuron comes close to an effector (a muscle or a gland). When a nerve impulse reaches the synapse, neurotransmitters cross the tiny gap between the neuron and the effector and stimulate the activity of the effector.

Neurotransmission at a Synapse

The autonomic nervous system contains two divisions. The sympathetic system stimulates our body during an emergency. The parasympathetic system returns conditions to normal after the emergency and relaxes the body.

Sympathetic Neurons and the Adrenal Medulla

Sympathetic Neurons and Fight or Flight

Some sympathetic neurons can trigger the flight or fight response on their own without stimulating the adrenal gland. They release noradrenaline as a neurotransmitter. The chemical travels through the tiny gap between the neuron and the target cell. It then joins to special receptor molecules on the cell membrane of the target cell, which are called adrenergic receptors, and triggers fight or flight reactions.

The Adrenal Medulla and Fight or Flight

Other sympathetic neurons stimulate the adrenal medulla to release noradrenaline and adrenaline into the bloodstream. The hormones then travel around the body in the blood. They trigger fight or flight reactions after binding to adrenergic receptors on target cells.

Neurons in the Autonomic Nervous System

A sympathetic neuron actually consists of two shorter neurons, one leading to the other. (The same situation applies to parasympathetic neurons.) The long extension of each sympathetic neuron is often known as a fiber. A structure called a ganglion is located between connecting fibers, as shown in the illustration below.

The fiber of the first neuron is called the preganglionic fiber. It releases a neurotransmitter called acetylcholine. This chemical causes the stimulation of the second neuron and its fiber, which is known as the postganglionic fiber. The postganglionic fiber sends the nerve impulse to an effector. The fiber stimulates the effector by releasing noradrenaline as a neurotransmitter.

The preganglionic fibers are colored orange in the above illustration. The postganglionic fibers are colored yellow. The illustration shows that the fiber going to the adrenal medulla is a preganglionic one.

Noradrenaline: A Neurotransmitter and a Hormone

It might seem puzzling that noradrenaline can be released by both sympathetic neurons as a neurotransmitter and by the adrenal gland as a hormone. The chemical has the same structure and function in each case, so to some people it may seem as though the body has developed two different ways to perform the same task.

The explanation is that the body has really developed only one way to produce noradrenaline, since adrenal medulla cells are modified neurons of the sympathetic nervous system. A sympathetic neuron that goes to the adrenal medulla contains a preganglionic fiber. This releases acetylcholine, which stimulates a postglanglionic fiber in the adrenal medulla. The adrenal medulla fiber then releases noradrenaline. The noradrenaline from the adrenal medulla is the same chemical as the one released by sympathetic neurons, but since it's sent into the bloodstream it's called a hormone instead of a neurotransmitter.

Adrenaline is used as a medicine to treat a dangerous body-wide allergic response called anaphylaxis. The medicine may be referred to as epinephrine in this situation. The information about anaphylaxis given below is intended for general interest. Anyone who may have to use an adrenaline auto-injector must be under the care of a doctor, who will be able to answer questions.

Anaphylaxis Symptoms and Treatment

People with a serious allergy may carry an adrenaline/epinephrine auto-injector around with them. This device must be prescribed by a doctor. During a severe allergic response, life-threatening changes may take place in the body very soon after the person is exposed to the allergen—even within seconds.

Possible Symptoms of Anaphylaxis

Symptoms of anaphylaxis may include wheezing and difficulty in breathing. Blood pressure often falls to a dangerously low level as blood vessels dilate and become "leaky", losing fluid to their surroundings. The patient may also feel faint and experience sweating, swelling of the face or throat, hives, itching, stomach cramps, nausea, vomiting, diarrhea, and an irregular heartbeat.

Treating Anaphylaxis With an Auto-Injector

Some automatic injection devices are called adrenaline injectors while others are called epinephrine injectors. They both contain the same chemical and can be injected through clothing. The general procedure is to remove the cap or safety release, position the injector over the outer thigh, and then press the device into the thigh muscle. The injector must be left in place for about ten seconds. This enables a pre-measured dose of adrenaline to enter the person's body. The instructions for a specific injector may vary slightly, however. They should be read carefully before an emergency happens.

Common brands of auto-injectors are the EpiPen®, the Twinject®, and the Anapen®. It's very important that a person who has an adrenaline injector knows how to use their specific device. People who regularly come into contact with the person, such as family members and teachers, should also know how to use the device, where it is stored, and symptoms that require its use.

Effects of Adrenaline on Anaphylaxis

The adrenaline from an auto-injector expands constricted air passages by relaxing the muscles around them, allowing the patient to obtain oxygen. It narrows blood vessels in many parts of the body and stimulates the heart to beat more strongly, helping blood pressure to rise. It also relieves swelling and itching. Even if the injected adrenaline seems to have removed the symptoms of anaphylaxis, however, the affected person must go to hospital after the injection.

Adrenaline is used a treatment for other medical problems, including cardiac arrest. In these situations, it must be administered by a medical practitioner.

Understanding the Functions of the Hormones

Hormones are fascinating chemicals to explore. The behavior of adrenaline and noradrenaline is complex, interesting, and sometimes puzzling. Adrenaline has opposite effects in different parts of the body, for example. It causes blood vessels in the skin to constrict but ones in the skeletal muscles to dilate.

Adrenaline and noradrenaline are major hormones and adrenaline is a very important medicine, so it's worth trying to understand the roles of the chemicals in our lives. I hope researchers make some significant and useful discoveries about the substances in the near future and that the discoveries prove to be very useful for people that need medical help.


This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: What would happen if the adrenal gland did not produce adrenaline during an emergency situation?

Answer: There would be many consequences, since adrenaline in such an important hormone during an emergency. If you examine the "Effect" and "Benefit During an Emergency" table in the article, you will be able to discover some of the major consequences of the hormone's absence.

Question: What would happen if adrenaline continued to flow through your body?

Answer: Anyone who suspects that they are making too much adrenaline should visit a doctor for help. The Mayo Clinic page linked to below describes some potential problems of a stress response that doesn’t stop. I think it’s a good page to read, but people should still seek their doctor’s advice. Adrenaline is a helpful hormone, but if it’s constantly at a high level, health problems may result.

© 2012 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on October 29, 2017:

Hi, Eith. Adrenaline is released during stress or strong emotion whenever it's needed. The effect is rapid but doesn't last for long. It doesn't fit your description of a reserve battery, except in the sense that the adrenal glands have more adrenaline to release when this is necessary.

Eith on October 27, 2017:

I came across your article when searching for information that might explain how in times of great need I find I have the energy to do things that I can't normally do. I visualise a 'reserve battery' that seems to kick in. The 'fight or flight' response doesn't quite explain this as sometimes I may be needed in a family emergency to do a lot more over a prolonged period. Does the adrenale system provide this type of energy response too? Thank you!

Linda Crampton (author) from British Columbia, Canada on October 07, 2017:

Hi, Gene. Strong emotions can trigger adrenaline release. Listening to certain music and playing particular video games could create sufficiently strong emotions. I would ask a doctor whether it's advisable to do this repeatedly.

Gene on September 30, 2017:

Hi Linda I am hoping you can clear some things up for me. Just today I decided do some exercise, so I decided to use the elliptical in the living room.Exercise is boring to me so I decided to not only play video games but to listen to music as well. I'm normally exhausted by 20 to 30 minutes but this time I went for an entire hour. This peaked my curiosity so I did a little research. I can't vouch for the credibility of the sources but from what I read, it is possible for the body to make adrenaline as a response to playing certain video games and listening to certain music.If this is the case, is it healthy to continue taking advantage of adrenaline in these circumstances.

Linda Crampton (author) from British Columbia, Canada on March 14, 2013:

Thanks for the visit and the comment, ryanjhoe.

ryanjhoe from Somewhere over the rainbow on March 13, 2013:

I have panic attacks a few weeks ago and many sources says that it has to do with my adrenaline balance that filled up my body but I think I can handle it now. Thanks for sharing this!

Linda Crampton (author) from British Columbia, Canada on December 14, 2012:

Hi, BlissfulWriter. Thanks for the comment. The production of cortisol by the adrenal cortex and the effects of cortisol on our bodies would certainly be interesting topics for another hub! Adrenal fatigue is an interesting idea, too. At the moment it’s popular with alternate medical practitioners and isn’t generally accepted by mainstream medicine. That situation may change in the future, though, as scientists do more research.

BlissfulWriter on December 14, 2012:

Good article. And very relevant as our high-stress societies is causing many people to have what is known as "adrenal fatigue". The adrenals also produce one of our important hormones known as cortisol.

Linda Crampton (author) from British Columbia, Canada on December 14, 2012:

Thank you for the visit, Nell. I appreciate your comment and share very much!!

Nell Rose from England on December 14, 2012:

A really fascinating and useful look at this part of our bodies, amazing read, and the affects of adrenaline graph was so useful, voted up and shared, nell

Linda Crampton (author) from British Columbia, Canada on December 13, 2012:

I agree, Deb - the human body is very complex and so amazing! Thanks for the comment.

Deb Hirt from Stillwater, OK on December 13, 2012:

It amazes me how the complexity of our body can control so much.

Linda Crampton (author) from British Columbia, Canada on December 13, 2012:

Thank you very much for the comment, drbj. As always, I appreciate your visit!

drbj and sherry from south Florida on December 13, 2012:

If I were preparing to take a test about the Adrenal Gland, Alicia, I would find this hub immensely useful. Probably more useful than a text since you have encapsulated so much important information into these few paragraphs. Thank you for your assiduous research, m'dear, as always.

Linda Crampton (author) from British Columbia, Canada on December 13, 2012:

Thank you so much, Bill! I appreciate your visit. I think that the way the human body works is very interesting. It's a fascinating topic to study.

Bill Holland from Olympia, WA on December 13, 2012:

Wow! You really know your stuff. I could not sooner write a hub like this than I could fly to the moon flapping my arms. Great information here Alicia!