The Body's Stress Response - The Fight or Flight!

The Stress Response

Stress can come in many forms such as:


  • a looming deadline at work

  • a persistent worry about losing a job

  • concerns about possible job cuts or company reorganization

  • a belief that you may not be able to continue to pay your bills

  • suddenly realizing that you are stuck in an elevator

  • the moment you realize you’ve lost your wallet

  • a barking dog suddenly pops out from behind a parked car, as you are walking by.

The typical stress response can present with physical symptoms such as the heart pounding, breath quickening, muscles tensing, especially in the neck, shoulders and back and beads of sweat may appear. This type of response is known as the Fight-or-Flight-or Freeze Response. It evolved over hundreds of years as a much-needed survival mechanism, enabling people and other mammals to react quickly to life-threatening situations. This ‘stress response’ is carefully orchestrated yet shows up almost instantaneously when the perceived threat presents itself.


Unfortunately, the stress response can also appear when there is a not-so-dangerous situation, such as:

  • a traffic jam

  • family disfunction

  • relationship issues.



Science has shown that stress over long periods of time, can be detrimental to the health and wellness of the individual. Over time, the activation of the stress response takes a toll on the body because, it’s been proven that stress contributes to high blood pressure; promotes the formation of artery-clogging deposits, and causes the brain to change. (1) These changes may contribute to anxiety, depression and addiction. More preliminary research suggests that chronic stress may also contribute to obesity, both through direct mechanisms (causing people to eat more) or indirectly (decreasing sleep and exercise).


The Mechanics of the Stress Response!


When there is a perceived threat or danger, thus invoking the stress response, many intricate functions happen in the brain almost instantly, involuntarily, and all before the person becomes aware.


The Body's Stress-Response Steps:

1) Distress messaging and signals are sent out from the amygdala of the brain to the hypothalamus, which functions like the body’s Head Quarters.

2) At Head Quarters, the messaging is communicated to the rest of the body, using the nervous system. Suddenly the person has the ability and the energy to fight or flee.



3) Involuntary body functions begin to happen such as increased breathing, increased heart rate, increased blood pressure, dilation or constriction of key blood vessels and small airways in the lungs called the bronchioles.


4) The Autonomic Nervous System, (ANS) consisting of the Sympathetic (SNS) and Parasympathetic (PNS), Nervous systems is engaged. Think of an automobile. The SNS can be likened to the gas pedal and the PNS, is more like the brake. The SNS functioning like the gas pedal triggers the fight-or-flight response, providing the body with a burst of energy so that it can respond to a perceived danger. The PNS, the brake in the car, promotes the “rest and digest” response that calms the body down once the danger has passed.

5) Back at Head Quarters, (Hypothalamus), the SNS is activated and a distress signal is sent through the autonomic nerves to the Adrenal Glands.

6) The Adrenals respond by pumping a hormone called Epinephrine (also known as Adrenaline) into the bloodstream. It circulates through the body, brings on a number of physiological changes. One of those changes is that there is an increase in heart rate as it pushes the blood to the muscles, the heart and the other vital organs. Pulse rate and blood pressure, also increase.

7) The person having these changes begins to breathe faster; small airways in the lungs begin to open up wide allowing the lungs to take in as much oxygen as they possibly can. Any extra oxygen is sent to the brain which allows for heightened alertness. Sight, hearing and other senses become acute.


8) Meanwhile, Epinephrine has triggered the release of blood sugar (blood glucose) and fats from temporary storage sites around the body. The glucose and the fats flood into the bloodstream, supplying energy to all parts of the body.


NOTE: All of these changes happen without the person’s awareness, in fact, the initial responses of the amygdala and hypothalamus is so perfectly orchestrated that the brain’s visual centers have not even had an opportunity to process what is actually happening. This is why people are able to jump out of the path of an oncoming car even before they think about what they are doing.


9) As the initial surge of epinephrine subsides, and if the perceived threat is still there, Head Quarters activates the second component of the stress response system, known as the HPA axis. This network of key players consists of the Hypothalamus, the Pituitary Gland (sometimes referred to as the Master Gland) and the Adrenal Glands.

10) This HPA axis relies on a series of hormonal signals to keep the SNS (the gas pedal) pressed down. If the brain continues to perceive something as dangerous, Head Quarters releases Corticotropin-releasing Hormone (CRH). CRH travels to the Master Gland which triggers the release of Adrenocorticotropic Hormone or (ACTH) which travels to the adrenals, prompting them to release Cortisol.

11) The body remains revved up, on high alert. When the threat passes, cortisol levels fall and the Parasympathetic Nervous System (PNS), the brake, dampens the stress response.


Sometimes, the body stays in a stress response state, even though the perceived threat is gone. When stress levels remain above normal levels over an extended period of time, this is a good time to give your Parasympathetic Nervous System and more specifically, your vagus nerve a little boost.







Contributions from:

1) Dr. Herbert Benson, Director Emeritus of the Benson-Henry Institute for Mind Body Medicine, at Massachusetts General Hospital

2) Harvard Health Publishing

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