STRESS – What happens on a physiological level?

The concept of stress was first applied to a physiological state of arousal by Canon (1914), who proposed that for an organism to function at optimal level it must possess the ability to maintain a stable internal environment (homeostasis). Any force which acted to disturb the homoeostatic state was defined as a stressor.

The stress response is a complex physiological event which results in metabolic, neuroendocrine and behavioural changes. Stress is determined by “the balance between the perceived demands from the environment and the individual’s resources to meet those demands” (Frankenhaeuser, 1986; Lundberg, 1995).

When the body feels threat or harm, the sympathetic nervous system becomes aroused to aid in the body’s ability to cope with difficulties. During this time the parasympathetic nervous system relinquishes control of the body so that the body is able to make a physical response to protect itself. The autonomic nervous system provides the rapid response to stress commonly known as the fight-or-flight response, engaging the sympathetic nervous system and withdrawing the parasympathetic nervous system, thereby enacting cardiovascular, respiratory, gastrointestinal, renal, and endocrine changes.

Once the brain has decided there’s a danger, the hypothalamus sends signals down the spinal cord to the pituitary gland at the bottom of the brain, telling it to produce more adrenaline and cortisol and release them into the bloodstream. These hormones speed up heart rate, breathing rate, blood pressure, and metabolism. Blood vessels widen to let more blood flow to large muscle groups, putting our muscles on alert. Pupils dilate to improve vision. The liver releases glucose to sustain muscular activity. Sweat is produced to cool the body and blood flow is regulated away from less important organs to the muscles to prepare for a fight (Payne, 2004, Benson, 2000). All of these physical changes prepare a person to react quickly and effectively to handle the pressure of the moment.

This reaction helps us survive by running away from an attacking predator or fighting off a rival interested in our mate. In modern times, we don’t have to worry about fighting off dangerous animals, but the stress response gets activated when faced with conflicts at work, having disputes with friends or family members or even while driving. When the fight-flight response is activated, we tend to perceive everything in our environment as a possible threat to our survival. As the fight-flight response bypasses the rational mind and moves us into “attack” mode we may overreact to the slightest comment. Our thinking becomes distorted and we see everything through the filter of possible danger.

The stress response is priming us for action (fighting or fleeing) but when we can not act on it because we have to sit at our desk and “control ourselves” or “freeze” and adrenaline along with the unfinished action gets stuck in our bodies. As a result we get triggered more easily which casues us to become aggressive, hypervigilant and over-reactive. This has a negative effect on our immune and digestive system, as well as overworking the heart.

Excess stress does not always show up as “feeling stressed”. It may manifest as physical symptoms such as “eye twitching” and “teeth-grinding.” On the other hand, we may “feel” lots of emotional stress and experience few physical symptoms.

By becoming more aware of and recognising the symptoms and signs of being in fight or flight (e.g. muscle tension, headache, upset stomach, accelerated heartbeat, poor concentration or shallow breathing) we can begin to handle stressful situations better.


Baker, D. B., & Karasek, R. A. (2000). Stress. In B. S. Levy & D. H. Wegman (Eds.), Occupational Health – Recognizing and Preventing Work-Related Disease and Injury (pp. 419-435). Philadelphia: Lippincott Williams & Wilkins.

Cannon, W.B. (1914). The emergency function of the adrenal medulla in pain and the major emotions. American Journal of Physiology, 33, 356-372.

Frankenhaeuser, M. (1986). A psychobiological framework for research on human stress and coping. In H. H. Appley & R. Trumbull (Eds.), Dynamics of stress: Physiological, psychological and social perspective (pp. 101-116). New York: Plenum Press

Lundberg, U. (1995). Methods and applications of stress researach. Technology and Health Care, 3, 3-9.

McEwen, B. S., & Sapolsky, R. M. (1995). Stress and cognitive function. Current Opinion in Neurobiology, 5, 205-216.


About Mensch - Connecting Mind Body Breath

I am committed to provide empowering information, to help you cope with painful emotions and support you towards personal growth and development. I combine my PhD in Psychology with 15 years of practical experience in counselling across clinical, corporate and community settings. Contact me on 0426 558 562 for a FREE 10-minute phone consultation to talk about your needs or write me a quick email at
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