The Science of Stress

by | Oct 5, 2018 | Mental Health + Happiness


We all feel it. But what is it?

Having a deeper understanding of stress can help us to overcome and manage its adverse effects on our body and mind.

Signs and Symptoms of Stress

The psychological symptoms of stress include feeling overwhelmed, worry, fear, anger, tearfulness, irritability, anxiety, helplessness and/or memory problems.

Physical symptoms include heart palpitations, fatigue, stomach upset, diarrhoea, headaches, muscular aches and pains, weakened immune system and/ or high blood pressure.

Behavioural symptoms of stress include difficulty concentrating, fatigue, lacking motivation, sleep disturbance, insomnia, social withdrawal, unhealthy eating habits and/or short temper.

Sound familiar?

Definitions of Stress

The dictionary has several definitions of stress, including:

“Pressure or tension exerted on a material object,”
A state of mental or emotional strain or tension resulting from adverse or demanding circumstances” and
Physiological disturbance or damage caused to an organism by adverse circumstances.”

A stressor is anything that affects one’s well being or survival, and stress is a natural human response to a stressor designed to bring us back to homeostasis. Homeostasis is the way in which the body maintains its internal equilibrium for well being and survival.

The stressor can be an external threat, for example a bomb going off or loosing your job, or it can be internal, like feeling time pressured or worried about the way you’re perceived by your colleagues.

Acute and Chronic Stress

Stress can be acute, in greater or lesser degrees. Mild acute stress, like starting a new job or giving a presentation, can lead to developing an adaptive response to meeting life’s challenges, but severe stress, like being exposed to a violent and life threatening crime, can lead to Post-traumatic Stress Disorder or other mental health problems.

Chronic stress, on the other hand, is stress that continues over an extended period of time, such as chronic health issues, relationship difficulties, financial problems, bullying, social isolation or living in an unsafe environment.

The Physiology of Stress

The body’s stress response kicks in as soon as we realise the presence of a stressor. Signals are sent to the brain and hormones are released in order to cope with the stress. The energy demands of the body are shifted from long term processes, like digestion, tissue growth and sexual functioning to processes that enable to us to deal with the situation at hand, including utilising muscles required for action, oxygen in the lungs, decreased pain sensitivity, and reduced tendency to bleed.

The hormonal response to stress happens along the HPA (hypothalamic–pituitary–adrenal) axis. The hypothalamus, pituitary gland and the adrenals glands control our reactions to stress, and are responsible for many body processes like digestion, immune functioning, mood, sexuality and energy.

The hypothalamus, the command centre at the base of the brain, is stimulated by the amygdala, an almond shaped set of neurons, located deep in the brains medial temporal lobe, which plays a key role in both the fear response and pleasure. The hypothalamus then excites the pituitary gland, a pea size master gland that sits behind the nose, whose main function is to secrete hormones into the blood stream, regulating many of the bodies vital functions.

The pituitary gland then alerts the adrenal glands, a triangle shaped gland that sits on top of the kidneys, and the adrenal medulla (the inner part of the gland) secretes the neurotransmitter adrenaline (epinephrine), which instigates the fight-or-flight response. This results in an increase in pulse rate, sending more glucose and oxygen to the brain (to keep you more alert), muscles and lungs, a constriction and release of protein in blood vessels to assist with clotting, and a conversion of glycogen to glucose and release of fatty acids from fat stores to supply us with a ready source of available energy. The hormone cortisol is then released, to build back up energy reserves depleted by the surge of adrenaline, by converting food into energy storage with glycogen and fat. Cortisol can continue to be released for hours after the stressor.

Stress and the Autonomic Nervous System

The stress response also activates the Autonomic Nervous System, the part of the nervous system that is in charge of bodily functions, but is not under our conscious control. There are three main branches of the Autonomic Nervous System, the sympathetic, the parasympathetic and the enteric.

The sympathetic branch is activated during the stress response and is like an accelerator in a car, triggering the fight-or-flight response and providing the body with a burst of energy to respond to perceived dangers. The parasympathetic branch, on the other hand, promotes rest-and-digest is like the brake in the car, dampening the stress response once the threat has passed.

The enteric branch of the nervous system is not widely discussed, but actually has a similar number of neurons as the spinal cord and is sometimes called the little brain. The enteric nervous system is in embedded in the lining of the gut and orchestrates various digestive functions. It is adversely affect by stress.

When the parasympathetic branch of the autonomic nervous system kicks in, it prepares you to meet the stressor, including pupils dilating, heart speeding up, digestion slowing down and blood pressure rising.

Activation of the sympathetic nervous system is designed to save our lives in times of crisis, but if it is triggered too often, it can result in stress related disease, including mental health problems, cardiovascular disease, obesity, gastrointestinal problems and more.

Good Stress and Bad Stress

Stress has received a bad reputation, but a little bit of stress can actually be a good thing. It can help to keep us stay alive when we’re in danger and it can actually improve our performance.

Yerkes-Dodson Law (figure from Storost)

Based on the work of Robert Yerkes and John Dodson, the Yerkes-Dodson Law (1908) states that arousal (stress) improves performance up to a certain point, then performance reduces as arousal increases.

Optimal performance is achieved with a moderate amount of arousal.

Responses to Stress

In their book, The Science of Stress, Neuropsychiatrists Albert Yeung, Ana Ivkovic and Gregory Fricchione describe three typical responses to stress.

Firstly, the stressor and the individuals ability to respond may be well matched, and the response results in a return to homeostasis. This is likely to be a less severe or threatening stressor.

Secondly, the stressor may be excessive or continual and be greater than the individual’s capacity to respond. This results in vulnerability as a result of stress. This is likely to be more severe or ongoing stressor.

Thirdly, while the stressor may be excessive or ongoing, there is a good match between the stressor and the individual’s capacity to respond, leading to post-traumatic growth of anti-fragility. This is not always discussed in relation to stress and trauma, but is an important and powerful catalyst for growth and developing inner strength and wisdom.

Managing Stress

The good news is that there are many strategies that help to reduce, manage and prevent stress, including counselling, relaxation training, breath work, mindfulness based practices and meditation.

My personal favourites include practicing Embodied Rest, iRest Meditation, walking in nature, practicing yoga, spending time with friends and loved ones, and finding someone you can trust to talk to about stressful issues and creating a life you love.


Harvard Health Publishing. Understanding the Stress Response. Published March 2011, Updated May 2018.
Million, Mulugeta, and Larauche. Muriel. (2016). Stress, Sex and the Enteric Nervous System. Neurogastroenterology and Motility :The Official Journal of the European Gastrointestinal Motility Society. 28(9):1283-1289.
Pfeiffer, Ronald F. (2007). Neurology of Gastroenterology and Herpetology. In Neurology and Clinical Neuroscience. Edited by Schapira, Anthony. Chapter 114 (pp 1511 – 1524). Elsevier.
Storost, Konrad. (2016). Voluntary Takeover in Automated Driving.10.13140/RG.2.2.35185.68965.
Yerkes, Robert M., and Dodson, John D. (1908). The Relation of Strength of Stimulus to Rapidity of Habit-Formation. Journal of Comparative Neurology and Psychology, 18, 459-482.
Varvogli, Lisa and Darviri, Christina (2011). Stress management techniques: evidence-based procedures that reduce stress and promote health. Health Science Journal, 5(2), 74-89.
Yeung, Albert S., Ivkovic, Ana and Fricchione, Gregory L. (2016). The Science of Stress. Chicago: The University of Chicago Press.


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