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Stress and the Brain: Unpacking the Impact on Health


Imagine you have decided to drive your car home after having a few beers. As you approach a junction, you see a blue light flashing directly behind your car. It is the police. Your heart begins to beat much faster, your pupils dilate, and you feel knots in your stomach and you are short of breath. Psychologists call this stress. This essay will explain the direct correlation between psychology and physiology, and the physiological changes that take place in the body as a result of these perceptions. It will explain the function of the nervous system and the relationship it has with stress.

Stress is the body’s physical and psychological response to a sense of danger or harm. What is known as a stressor is seen as the direct root/cause of the stress, whether it is a psychological cause such as events and situations or a physiological cause such as pain or extreme hot or cold temperatures. These stressors cause an imbalance of the body’s homeostasis (Selye, 1956).


Stress is seen as a survival mechanism, an evolutionary adaption to environments filled with life-threatening dangers. The human body’s cascades of responses to stress are designed to get you away from danger, and so the body mobilises as a response to the danger.

The beginning signs of stress commence in the brain. Stress is not usually about whether we can actually cope with a situation, but more about our brains being aware of the demands of coping with a situation and the brain under estimating its coping abilities (Selye, 1956).

The transactional model of stress is a framework for evaluating the processes of coping with stressful events. The transactions seen in this model depend on the impact of the source of the stress, known as the stressor. When faced with a stressor, a person evaluates the potential threat. This stage is known as the primary appraisal. It is a person’s judgement about the significance of an event as being stressful, positive, controllable, challenging, or irrelevant. Shortly after facing the stressor, secondary appraisal follows, which is an assessment of the stressor and what can be done about the situation (Lazarus & Cohen, 1977).

What Are Stressors?

There are two main categories of stressors.

  1. Physiological stressors: these stressors put strain on our body. E.g. injury, hot/cold temperature, illness, pain.
  2. Psychological stressors: These are situations, events, individuals, and comments, which are interpreted as negative or threatening.

The physiological responses to stress shown above are the body’s method of defence. The heart rate increases to raise the amount of oxygen that goes to the brain, so that your body and thoughts move faster. The reason for pupil dilation is that the autonomic part of the nervous system dictates the movement of the iris to restrict the amount of light that comes into the eyes, thus making it easier for a human or animal to escape from danger. The knots or “butterfly” feeling in the stomach is caused by there being more blood flow sent to the brain and restricted to the stomach.

The effects of stress on the body are complex, and can affect nearly every major system. Over the years, psychologists and scientists have learned how and why the body reacts to stress in these methods, and have also gained insight into the long-term effects that stress can have on a human’s physical and mental health. Research has proved that persistent stress contributes to high blood pressure and causes brain changes that can contribute to depression and anxiety. Numerous studies have also linked chronic stress to the addiction of drugs and alcohol and substance abuse.

The response to stress begins in the brain. The amygdala, hypothalamus, and cerebral cortex are referred to as the command centres of the brain. When a person senses an incoming point of danger, the eyes and ears send information to the amygdala. The amygdala interprets the pictures and sounds, and when it senses this information to be of danger, it at once transmits a signal of distress to the hypothalamus.

The Fight or Flight Response

Our bodies’ fight or flight response is the primary example of involvement of stress in survival. When we see a hungry animal suddenly attacking us in a forest, the fight or flight response switches on and prepares us to either run away or face the attacking animal. The body prepares for this by shutting down energy supplies to every system that is not involved in the fight or flight response.

The hormones which get released when we are stressed put our body into a fight or flight mode. This reads to reduction in activity of the advanced decision-making part of the brain known as the pre-frontal cortex. The two hormones, cortisol and adrenaline, mediate the following responses:

  1. Increase the heart rate and narrow the blood vessels. This results in increase in blood pressure and blood sugar, which results in increased oxygen delivery to the heart–lung system and the important flight muscles of our body.
  2. Increase in the amount of sweating to cool the hyperactive muscles.
  3. The blood gets thickened to increase oxygen supply (RBCs), enhance defense against infections (WBCs), and reduce the chances of bleeding (platelets).
  4. Sharpen the sensors, e.g., dilation of pupils and enhanced hearing.
  5. Help focus your attention completely on the threat and lead to exclusion of everything else. The body increases the blood supply to peripheral muscles, heart, and brain.
  6. Slow down or shuts off the irrelevant activities like digestive system and speech areas of the brain.
  7. Enhance secretion of endorphins, the natural pain killers of our body.

Regaining Homeostasis

When we look at the biological aspects of stress, it is seen as a threat to homeostasis. The body strives to maintain homeostasis even when there are stressors or aversive stimuli. In order to maintain this steady state, the body undergoes a very complex range of responses that involves nervous system, the endocrine, and immune systems. This is known as the stress response. There are a number of behavioural and physiological changes that take place in order for the body to brace up to the challenges in the environment. The body is on a high alert mode with a wide array of physiologic effects of the stress response.

When we consider the behavioural effects of the stress response, it consists of greater awareness, better cognition, excitement, and greater insensibility to pain. A situation is deemed stressful or dangerous when the hypothalamus, which is found at the "base of the brain," is activated and it signals the pituitary gland, and the adrenal medulla (Smith and Vale, 2006). The pituitary gland secretes the adrenocorticotropic hormone (ACTH) and ACTH, in turn, stimulates the adrenal glands to produce the hormone corticosteroid, which helps the body to maintain stable supplies of blood sugar to cope with the stressor. This process helps the body to regain normalcy.

The body responds with The Fight or Flight Response with the help of the Sympathomedullary Pathway (SAM). The Hypothalamic Pituitary-Adrenal (HPA) system is in charge of the stress response (Chrousos, 1992; Habib, Gold, and Chrousos, 2001; Sapolsky, Romero and Munck, 2000; Whitnall, 1993). Once the perceived ‘threat’ has ended, the parasympathetic takes control and brings the body back into a balanced state. This is in response to short-term stress and this response helps us survive danger.

The Effects of Chronic Stressors

However, the effect of long-term or chronic stressors is quite different. For example, during the process of releasing stored glucose from the liver (for energy) and controlling swelling after injury, the immune system becomes suppressed. Hence, the mind and body connect is most evident in our stress response. There is a clear and very straight connection between the stimulus in the environment and the immediate consequence on the mind and body.

Psychoneuroimmunology is an interdisciplinary subject dealing with the study of the immune system, brain, and mind. Dr. Janice Kiecolt-Glaser has, in recent times, contributed considerably to this subject with her inputs about how “How Stress Kills: New Perspectives on Stress and Inflammation (Waring, 2008)". She has established a very fundamental relationship between stress and diseases. Within our body, cytokines and interleukins transmit messages essential to the immune responses. A part of that response is inflammation. It is one of the body’s normal defences against injury, infection, irritation, or surgery. However, inflammation is not similar to infection. The body requires good inflammation, because the cytokines signals to the immune cells. With acute inflammation, positive effects occur. However, chronic inflammation is associated with "tumor cell survival” and other problems. Chronic stress can cause dysregulation in the immune system and result in increased risk of disease. This, in turn, raises the proinflammatory cytokines, namely the interleukin-6 (IL-6).

Working with her virologist husband Dr. Ronald Glaser, Dr. Janice Kiecolt-Glaser has used her experience as a clinical psychologist to conduct clinical trials on a varied population of aged people, young students, couples, women, and caregivers. She showed that chronic stress can significantly hasten ageing and can result in associated changes in IL-6, which is a cytokine related to some types of cancers and heart diseases (Waring, 2008). It could also lead to arthritis, type II diabetes, and osteoporosis. Stress also can cause weakened vaccine responses in older adults. Young people affected by exam stress were affected too. Oral wounds took longer to heal when students felt stressed and anxious about their exams, whereas wounds healed faster when they were on vacation (The Ohio State University, 2015).

Studies on couple relationships and endocrine health functioning showed that conflicts in their relationship had negative impacts on their health (The Ohio State University, 2015). Interpersonal stress seemed to largely affect women more. Similarly, caregivers who underwent considerable stress in caring for their partners showed an increase in Il-6. Caregivers have very little control over their lives because their partner's health is not predictable and the stress they experience can be overwhelming.

Her lab studies have revealed that daily stressors, marital friction, and major depressive disorder may have consequences on the behaviour of the individual, which, in turn, can affect their health adversely (Waring, 2008). Thus, obesity could be caused by the high-fat meals and low level of exercise occurring as a pattern due to depression, and this obesity could lead to health issues. Depression, poor physical fitness, and obesity are all linked and can lead to higher levels of inflammation.

In another study, she has made an interesting link between mood and obesity and their interactions to show maladaptive responses to fast-foods, which are meals with high saturated fat. This, in turn, boosts" post-meal inflammation" and "triglyceride responses" that are linked with cardiovascular risk. In other words, symptoms of depression can interact with diet to add to inflammation. Depression, diet, inflammation, and cardio vascular diseases are related (Waring, 2008).

Kiecolt-Glaser says that there is a vicious pattern found in people undergoing stress. "The stressed get more stressed, serving as substrate for more inflammation. They are primed to respond more strongly to subsequent challenges (Kiecolt-Glaser, 2015).” She adds that stress makes us follow poor "health behaviours" and sleep deprivation can increase IL-6. She refers to 'Adipose belly fat' as IL-6 factories because it secretes as much as thrice the levels of IL-6. She adds that even mild-to-moderate physical activity can aid in easing inflammation. However, because people are stressed, they do not want to do exercise.

Few Case Studies

In one experiment, when rats were subjected to external stress, they developed depression. When scientists compared the brains of these stressed rats to normal ones, they found the new brain cells produced by the stressed rats were fewer in number than in the normal ones.

This experiment is useful in shedding light on the fact that the mind is affected by stress adversely. The rats were a valid sample for use in the experiment because the rats could respond to stress in the same way as humans do (Hildebrandt, 2012).

Janice conducted a natural experiment with seventy-five medial students. They were questioned one month before their exams and on the first day of their final exams. Blood samples from the students were also collected.

The questionnaire (and blood samples) reveals that the immune system was suppressed when high levels of stress were felt by the students, who complained about the stress symptoms in the form of having felt feelings of loneliness and sadness.

The sample used in the study is valid as the studied subjects were medical students who were capable of indentifying stress symptoms better than the normal population. The results found about the stress–immunology suppression effect can be extended to the general population too.

Stress and Type A/B Behaviours

Two cardiologists, Friedman and Rosenman (1974), worked on the hypothesis that the personality type of an individual decides response to stress. According to them, individuals with Type A personality were by, nature, highly competitive, self-critical, impatient, and aggressive, driven by a sense of urgency that did not allow them to relax (Friedman and Rosenman. 1974). Individuals with Type B personality were less prone to anxiety and were content to give rein to their imagination, making them more creative.

Individuals with Type A personality are more likely to experience stress in most situations and give a fight or flight response to the threat they perceived from the environmental stimulus (McLead, 2008). Interestingly, some studies have shown that individuals with Type A personality are more likely to perceive hostility and the stress hormone is more active in them than in personality Types B or C. The study suggests that hostility is a major cause for cardiovascular diseases (Rosenman, 1976). Individuals with Type B personality, on the other hand, are not competitive or combative, willing to do things slowly at their own pace and willing to express their feelings. Individuals with Type C are extreme in their conflict avoidance and are generally 'pathologically nice.'

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Thus, the mind and body connect is most evident in our stress responses. Stress responses that begin in the brain’s hypothalamus involve subsequent release of glucocorticoids that mediate appropriate reactions of the body to the stressors. Acute stress responses help the body regain the lost homeostasis in the face of danger and threats. However, chronic stress responses have been linked to cardiovascular diseases. Depression and mood have also been linked to obesity and stress levels. Thus, the connections between the mind and body are well established while mediating stress responses.


  • Chrousos, G. P. (1992). ‘Regulation and dysregulatïon of the hypothalamic-pïtuitary-adrenal axis. The corticotropin-releasing hormone perspective.’Endocrinol Metab Clin North Am., vol. 21, pp. 833–858.
  • Friedman, M., and Rosenman, R. (1974). Type A Behavior and Your Heart. New York: Knopf.
  • Habib, K. E., Gold, P. W., and Chrousos, G. P. (2001) ‘Neuroendocrinology of stress.’ Endocrinol Metab Clin North Am., vol. 30, pp. 695–728.
  • Hildebrandt, S. (2012), How Stress Can Cause Depression, Available at[Accessed 26 Oct. 2016].
  • Kiecolt-Glaser, J. K., et al., (2015). ‘Inflammation: Depression Fans the Flames and Feasts on the Heat,’ Am. J. Psych. Vol. 172, no. 11, pp. 1075-1091.
  • Lazarus, R. S. and Cohen, J. B. (1977). “Environmental Stress”. In I. Altman and J.F. Wohlwill (eds.), Human Behavior and Environment. (Vol 2) New York: Plenum.
  • McLead, S. (2008), ‘Type A Personality,’, Available at>[Accessed 26 Oct. 2016].
  • Rosenman, R. H., Brand, R. J., Sholtz, R. I., and Friedman, M. (1976). ‘Multivariate prediction of coronary heart disease during 8.5 year follow-up in the Western Collaborative Group Study.’ The American Journal of Cardiology, vol. 37, no. 6, pp. 903-910.
  • Sapolsky, R. M., Romero, L. M., and Munck, A. U. (2000). ‘How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.’ Endocr Rev., chronic stressors vol. 21, pp. 55–89.
  • Selye, H.(1956). The Stress of Life. New York: McGraw-Hill.
  • Smith, S. M. and Vale, W. W. (2006). ‘The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress,’ Dialogues Clin Neurosci., vol. 8, no. 4, pp. 383–395.
  • The Ohio State University (2015), Janice Kiecolt-Glaser, Available at [Accessed 26 Oct. 2016].
  • Waring, B. (2008), Kiecolt-Glaser Offers New Paradigm on How Stress Kills, Available at[Accessed 26 Oct. 2016].
  • Whitnall, M. H. (1993). ‘Regulation of the hypothalamic corticotropin-releasing hormone neurosecretory system.’ Prog Neurobiol; vol. 40, pp. 573–629.

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