Components of our stress response system include the brain: the visual cortex, thalamus, amygdala, and hippocampus. The central nervous system (CNS) comprises the brain and spinal cord. The autonomic nervous system (ANS) includes the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
Glands involved are the hypothalamus-pituitary-adrenal (HPA) axis, with the hypothalamus and pituitary residing in the brain, and the adrenal glands sitting on top of both kidneys. Each adrenal gland has an outer cortex, responsible for releasing long-term stress hormones, and an inner medulla responsible for releasing short-term stress hormones.
Hormones involved include noradrenaline, adrenaline, corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, dopamine, and GABA.
Our stress response system involves our entire body, including all organs and the brain/mind. It influences other organ systems, such as the digestive, immune, and circulatory (bloodstream) systems. When we over-activate this system, we risk causing our own physical and mental health issues. So, how does it work?
When we perceive something or someone as threatening, we send all sensory information to the thalamus. The thalamus relays this information to the amygdala, which processes all our emotions, detects the “danger signal”, and immediately signals the hypothalamus to activate the sympathetic nervous system (SNS) – our acute stress response. Simultaneously, it instructs the hippocampus to store all memories related to the fearful event, helping us avoid similar threats in the future. The hypothalamus activates the SNS by sending a signal down the spinal cord to the adrenal medulla to release noradrenaline and adrenaline into the bloodstream, to prepare the body and mind for danger.
Adrenaline and noradrenaline divert blood away from our core, strengthening our arms and legs while reducing memory recall and slowing digestion and immune responses. Blood is redirected from the skin, leading to less bleeding from cuts and increased flow to the arms, legs, shoulders, eyes, ears, and nose. Breathing speeds up as smaller airways in the lungs expand to absorb more oxygen.
Heart rate and blood pressure increase as the heart pumps blood and hormones faster through the body. Pupils dilate to improve vision and take in maximum light. The mouth becomes dry because the production of gastric juices and saliva is reduced. Muscles tense up, and the urge to run or fight intensifies. Our biology, physiology, and psychology all shift into defence mode to ensure we survive the threat.
The body and brain are now on high alert because the brain is focused on the stressor and its consequences. All these changes are brought about in the span of a single heartbeat by adrenaline and noradrenaline.
If the perceived danger passes and breathing calms, the brain activates the parasympathetic nervous system (PNS) to counter the effects of the SNS and bring the body and brain back to a state of rest, repair, and relaxation. This is the most vital part of our stress response system.
Sadly, most of us block this process by remaining in the stress response for too long. Nothing is more important to our physical and psychological health than allowing our PNS to take over. This means taking time after each stressor for the body and brain to recover and repair.
Chronic stress occurs when the body and mind are constantly responding to stressors in our salient domains – home, work, family, friends, health, finances, and community – and are unable to fully recover. This prevents the brain from activating the parasympathetic nervous system. When the brain cannot activate the PNS, it triggers its secondary defence, the hypothalamic-pituitary-adrenal axis (HPA axis), which prolongs and intensifies all the biological, physiological, and psychological changes caused by the sympathetic nervous system.
This is our long-term chronic stress response – the stress-illness link – that inflames organs, shuts down vital health systems, and leads to physical and mental illnesses.
In chronic stress response, the brain instructs the hypothalamus to release CRH (corticotropin-releasing hormone), which travels to the pituitary gland and stimulates the release of ACTH (adrenocorticotropic hormone). This hormone travels down the spine to the adrenal cortex, prompting the release of cortisol, our strongest steroid hormone, that helps defend against chronic stress.
Prolonged cortisol production and high glucose levels damage the mind and body. The kidneys and heart must work very hard to circulate cortisol, which can lead to increased blood pressure, heart issues, circulatory damage and prolonged suppression of the digestive and immune systems; resulting in gastric and stomach problems, a weakened immune response, and reduced lymphocyte production; making us more susceptible to illness and delaying recovery.
Additionally, chronic fatigue wears down the body and mind, leading to depression, anxiety, and burnout.
Excessive and prolonged cortisol levels can cause eye problems, while high blood-glucose levels increase insulin, potentially leading to diabetes. Elevated cortisol levels disrupt leptin signalling, which helps regulate eating habits, immune function, fertility, and energy expenditure. Cortisol also blocks melatonin production, leading to sleep disturbances and disrupting the circadian rhythm.
Headaches, shoulder, neck, and back pain, as well as the breakdown of muscle, bone, and connective tissue, are increased in the chronic stress response. Reduced blood flow in the skin causes skin irritations and breaks down collagen and elastin, leading to ageing in women. Cytokines are out in full force now, increasing inflammation, the foundation of all our physical and mental illnesses.
Long-term cortisol production puts our body and mind into attack mode. Thinking becomes blurred, memory recall is severely impaired, and libido is severely decreased. This is the resistance stage of our stress response, when we attempt to regain control while still suffering the consequences of the stressor. If we allow this to continue, the next stage is burnout.
To maintain physical and mental health, all we need to do is think before activating this system and address our stressors. Deep belly breathing will soothe the brain and body, allowing the parasympathetic nervous system to carry out all repairs.
