When faced with stressful situations, the body develops a stress response, which involves interaction between different body systems to cope with the stressors. The stress response starts in the brain, where cognitive appraisal of perceived threats and stressors in the environment is mediated by the brain, to activate the responding cardiovascular, immune, and neuroendocrine processes.
Stress can be both good and bad for you – good in the short term when sporadic episodes of acute stress help heighten your performance during adverse or demanding circumstances, and bad in the long term due to the devastating effects of chronic stress on mental and physical health. The difference between good and bad stress lies in the duration of the stress.
Acute stress:
The well-known “fight-or-flight” response is a survival mechanism that prepares an individual to cope with an emergency. This response starts in the amygdala areas (one in each hemisphere) of the brain. The amygdala, which plays a primary role in decision making and emotional responses, sends a distress signal to the hypothalamus area (viewed as a command center) in the brain, from where an emergency response is sent through a network of nerves, part of the central nervous system (CNS), to the adrenal glands, which responds by releasing high doses of adrenalin into the bloodstream.
Adrenalin spikes immediately affects the body, such as causing acceleration of the heartbeat and raising blood pressure for improved blood circulation, dilating the pupils to allow more light into the eyes for improved vision, increasing respiration, and constricting blood vessels in the skin to limit bleeding from wounds, if any. The liver responds by releasing more glucose and free fatty acid levels into the bloodstream for energy, while the immune system is activated, and molecules called endorphins are released to reduce our perception of pain. While these responses give us super-senses and the ability to react instantly, it comes at a cost to the body, as some body systems need to shut down to enable the “fight-or-flight” response. Blood flow is restricted to the skin (ever noticed how pale you are in a scary situation?), as well as to the reproductive and digestive systems.
After the initial surge in adrenalin that activates the immune system, the brain signals the adrenal glands after about 20 minutes to release another hormone, called cortisol, which helps to regain balance by returning the immune system back to normal levels, to prevent the immune system from becoming overactive and potentially destructive.
The acute short-term responses to stress have no ill-effects on the body.
Chronic stress:
Elevated levels of cortisol over the long term, however, has ill-effects on physical and mental health, by suppressing the functioning of the immune system, or even failing to regulate it. Apart from predisposing us to viruses and infections, chronically elevated cortisol levels can cause resistance to cortisol in cells and tissues, leaving the door open to inflammatory related diseases or even autoimmune disorders, where the immune system attacks own body cells and tissues of the body, such as in multiple sclerosis.
Chronically elevated levels of cortisol also has other detrimental effects on the body, such as over-eating or binge eating with increased fat storage, leading to weight gain and reduced insulin sensitivity. It contributes to high blood pressure and the formation of artery-clogging deposits.
Profound effects on the brain include an increased interconnectivity between the emotional centers in the brain (causing a constant fight-or-flight response), with lower connectivity to the rational part of the brain. This can lead to illogical and hyper-emotional behavior patterns. Other effects on the brain can include brain cell shrinkage and premature brain cell death. The influence of these factors on brain functionality can result in poor memory formation, poor attention span, poor focus, and a decline in cognitive potential and motivation.
Chronic stress can damage genetic material (DNA), resulting in biological changes that speed up the process of aging, and increase the potential to develop chronic diseases and adverse health conditions.
The chemistry involved in the stress response:
Acute short-term stress responses for the fight-or-flight survival mechanisms are produced via the sympathetic nervous system, known as the sympathetic-adrenal-medullary (SAM) axis, which is involved with the release of adrenalin.
Longer term stress is regulated by the hypothalamic pituitary adrenal (HPA) system, known as the HPA axis, which is involved with the release of cortisol.
- The autonomic nervous system has two components, the sympathetic nervous system (which triggers the fight-or-flight response), and the parasympathetic nervous system (which calms the body down after the danger has passed).
- In the event of acute stress, the amygdala sends a distress signal, which then activates sympathetic nerve fibers supplying the adrenal medulla.
- When activated, the adrenal medulla secretes adrenaline into the blood stream and this hormone triggers the fight-or-flight reaction in the body.
- When the initial surge of adrenalin subsides, but the brain still perceives danger, the HPA-axis is activated.
- The hypothalamus releases corticotropin-releasing hormone (CRH) to the pituitary gland, a small, bean-shaped gland situated at the base of the brain.
- CRF binds to receptors on the pituitary gland, which is then stimulated to secrete adrenocorticotropic hormone (ACTH) into the bloodstream.
- ACTH binds to receptors on the adrenal glands and stimulates them to release the stress hormone cortisol, which keeps the body on high alert.
- Once the perceived threat is over, the cortisol levels drop. The parasympathetic system then acts as a brake that dampens the stress response and promotes the “rest and digest” response that brings the body back into a balanced state.
- Cortisol enables the body to maintain adequate and steady blood sugar levels, which protects and helps the body to return to a balanced state after the short term “threat” has passed.
- Chronic long-term stress, however, keeps the HPA system activated, causing continuous high levels of cortisol to be released, with dire consequences on physical and mental health, as discussed earlier.
- In the image below, LC refers to the locus coeruleus, an area of the medulla oblongata, which is part of the brain stem.
Other topics in the Stress Series include:
- Stress resilience.
- Techniques to manage stress.
- Stress in the workplace
Sources:
The Stress Code. From surviving to thriving. Author: Richard Sutton. Published 2018, Pan Macmillan South Africa. P 318.
Understanding the stress response. Published online and updated 1 May 2018. Harvard Medical School. (www.health.harvard.edu)
What is the stress response? Published 2010. Simply Psychology. (www.simplypsychology.org)
Medical Physiology. A systems approach. (Physiology Handbook). By Hershell Raff, Michael Levitzky, et al. Published 2011. McGraw Hill Medical. P 786.
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