Physiology of stress

How stress turns us mindless or how the body displaces the mind.

A brief insight into the physiology of stress

By Tom Meyers

Stress is the reaction of the body to a perceived threat (stressor) which can be real or imagined. When the stressor is perceived as life threatening the autonomic nervous systems is activated   known as the fight or flight response. This activates the sympathetic nervous system (SNS) while at the same time subduing the parasympathetic nervous system (PNS) and so triggering the physiological stress response. Activation of SNS and inactivation of PNS additionally increases respiration, heart rate and blood pressure but more about that later.

The physiological stress response is activated at the hypothalamus which releases CRH. CRH in turn activates the pituitary to release ACTH that via the bloodstream arrives at the adrenal cortex. This is is the so called HPA axis – the hypothalamic – pituitary – adrenal axis.

ACTH activates the release of adrenaline, noradrenaline and cortisol into the bloodstream to get the body ready to fight or flight.

So while parts of the body are activated other parts are being inhibited: Growth and tissue repair, reproduction system, pain perception (lowered), immune system, urine production, digestive system, cognitive function,…

I like to come back to ACTH and the activation of the stress hormones adrenaline and cortisol. Adrenaline (which is also activated by the SNS) will increase heart rate, contracts blood vessels in the periphery – which causes amongst other things sweating – and in the forebrain (Bruce Lipton Ph.D.),  tightening of the blood brain barrier (Robert Sapolsky Ph.D.), diverts blood glucose to the to be activated muscles and dilates the air passages. Cortisol backs up the activity of adrenaline in the course of minutes or hours and increases the release of glucose and fatty acids. Cortisol also interferes wit the function of the neurotransmitters that are responsible for cell to cell communication in the brain.

While cortisol will release glucose and increase metabolism, adrenaline redirects glucose to the areas that are essential for the fight or flight reaction. Therefore the stress hormones are responsible that less glucose is distributed to certain areas of the brain including the hippocampus which is the area for memory and the prefrontal cortex, the area for cognitive thinking.

Although there is initially an increased alertness and sensitivity, when the stress response continues to be activated glucose levels in he brain start to be depleted and due to hyperventilation oxygen release to the cells will decrease having a negative effect on memory and cognitive functions.

Normally cortisol levels in the blood is being regulated through a negative feedback mechanism triggered in the hippocampus? However when the hippocampus receives less glucose and oxygen due to the mechanism as described above it will not send that message to the adrenal gland to stop the production of cortisol. Cortisol’s side effects are that it accelerates the degeneration of the hippocampus therefore damaging it and contributing to the malfunctioning of it creating increased degeneration (Robert Sapolsky Ph.D.). Another side effect of increased levels of cortisol in the blood is the inhibition of the immune system.

In short when stress hormones keep on being released we become mindless and our immune system is being tampered with which can result in change of behavior.

This mindlessness is being reinforced by the increase in respiration that I mentioned before. The SNS will increase the breathing cycle disrupting the CO2 – O2 balance as more CO2 is being removed from the cells. This reduces blood flow to the brain as CO2 deficiency causes constriction of arteries and arterioles. Less blood means less oxygen, glucose and other nutrients. Also if CO2 concentration is low, O2 cells are stuck with red blood cells. Hence, CO2 deficiency leads to hypoxia or low oxygenation of the body cells (the suppressed Bohr effect). The more we breathe at rest, the less the oxygenation of our cells in vital organs, like brain, heart, liver, kidneys, etc.

In short increased respiration will not only change the inflow of O2 through vasoconstriction, but also O2 release is hampered by low CO2 concentrations (the Bohr effect). That further reduces brain oxygenation resulting in mindlessness and change of behavior.

More information about the physiology of breathing click HERE (

And What has BioMotions® Body-Coaching to do with this you might ask? It reverses the effects of stress and thus all the above through:

  • It relaxes ➙ regulates breathing ➙ thus balances CO2 – O2 levels ➙ creates vasodilation, more   O2 is released to the cells while at the same time more glucose and nutrients are available.
  • Although not proven it is not unlikely that it has an effect on the perception of a life threatening event  ➙ regulates physiological stress response
  • Activates PNS ➙ decrease in heart rate and blood pressure
  • Through facilitation of the sphenoid bone there is a direct soothing impact on the pituitary gland
  • Stimulates acupuncture points that are related to relaxation of the mind, reinforcing and improving brain function and pain reduction.
  • Creates vasodilation in the cortex (not proven)
  • Activates Neuro Vascular Points that are related to improved vascularization of the brain
  • Facilitates the Self-Healing mechanism
  • … and who knows what else

Note: Email from R. Sapolsky (who wrote the book “Why zebra’s don’t get ulcers.”) I received on 21/12/2010 as regards to my question if stress created vasoconstriction in the brain.

To my knowledge, there is not a marked decreased in blood flow to the brain (or even the forebrain with areas like the frontal cortex and hippocampus) with chronic stress, no vasoconstriction.


There are two things, however:


One is a tightening of the blood brain barrier, so that it is harder for nutrients to exit from the circulation into the extracelular space in the brain.


The second is a decreased ability of brain cells (both neurons and glia) in those regions to absorb glucose from that extracellular space. So different mechanical basis, but the same effect that I think you have in mind — some of the most cognitively critical parts of the brain having less energy available during chronic stress.


However B. Lipton in his book “Biology of belief” on p. 120 states: Adrenal stress hormones constrict the blood vessels in the forebrain reducing its ability to function. Additionally, the hormones repress activity in the brain’s prefrontal cortex, the center of conscious volitional action.

I bet both are right. Maybe tightening of the BBB looks like a constriction of the blood vessels. Vasoconstriction being done by contraction of the smooth muscles that line the blood vessels and BBB being created by endothelial cells with tight junctions.

I’ve written to B. Lipton for more info. When I receive it I’ll add the information here.


4 thoughts on “Physiology of stress”

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