Understanding stress - a biological perspective
Stress is defined in several different ways, with the simplest definition being that stress is a response that occurs “when pressure exceeds your perceived ability to cope” (Palmer & Cooper, 2014, p.7). As such, it is a response serves to help the person (or in fact any living object) deal with excess pressure (real or perceived) that disrupts physical or psychological equilibrium. It can therefore be argued that the stress response is a perfectly normal and helpful response, at least in the short term with it being an automatic reaction triggered by our senses in attempt to deal with danger, threat, challenge, or any demand.
The onset of a stress response can be a conscious belief that a situation is demanding to us OR it may also be an automatic subconscious reaction whereby our senses alert our brain to something that needs to be addressed in order to maintain balance (homeostasis). Examples of subconscious demands/pressures that our senses pick up on include things like hunger, temperature changes, exertion, insufficient sleep, or even something like loud noise. As such, it could therefore be the case that a person isn’t emotionally upset or distressed in order for their body to be in a stressed state. In fact, when it comes to chronic stress, or situations where people have been exposed to ongoing stress or trauma, it’s often the case that they have a muted appraisal of stress causing them to underestimate or discount a stressful situation to be ‘not that bad’ simply because they’re comparing it to something there were exposed to in the past. For example, someone may discount work related stress if they experienced a life altering or traumatic experience in the past. The issue here is that work-related stress resulting in long hours without sufficient rest or time for other life pleasures can be underestimated. Regardless of our interpretation of these types of situations, insufficient rest will be having a significant negative impact on the body via fatigue and/or poor energy intake.
Once initiated, the stress response is automatic and quite linear regardless of the source (physical or psychological). That is, the brain automatically releases neurotransmitters and hormones following a chain reaction in attempt to help the body tackle the demand/threat/danger, perceived or not (Palmer & Cooper, 2014; Hyland, 2014; Sapolsky, 2004).
This process is outlined in detail below
Demand/stressor is present = Brain activity increases, and the following occurs:
The cerebral cortex (where thought processes occur) AND the hypothalamus (the limbic part of the brain which controls or autonomic nervous system) are stimulated within seconds of being exposed to a stressoWhen this happens, a neurotransmitter called noradrenaline is released at the site of nerve endings and also from the adrenal medulla (found in the adrenal glands) causing adrenaline and noradrenaline to be released into the blood supply. Both of these neurotransmitters act on the cardiovascular, respiratory, immune and digestive systems within seconds resulting in increased heart rate, breathing and reduced blood flow to the gastrointestinal system (blood is needed elsewhere so digestion is not a priority).
In addition to these reactions, the anterior part of the hypothalamus also simulates a third part of the brain called the pituitary gland in order to initiate the release of three hormones (ACTH, Cortisol, and Aldosterone).
Adrenocorticotropic hormone (ACTH) is a hormone that is released into the blood to stimulate a second part of adrenal gland to release cortisol (as well as also releasing adrenalin and noradrenaline, outlined above). This process takes a slightly longer time to unfold compared with the almost instant release of adrenalin and noradrenalin, typically occurring a couple of minutes after the initial neurotransmitter response. However, this delay serves the purpose of helping the body to contend with ongoing demand should the stressor not be dealt with within the moment by the body’s physical responses meant to overcome the stressor. Cortisol does this by increasing arterial blood pressure, mobilising stored glucose in the form of glycogen (from the liver) and fats (from adipose tissue) as a source of fuel. Cortisol also helps to reduce inflammation associated with the initial heightened immune system response. Consequently, increased/ongoing raised cortisol can result in a suppressed immune system and the individual experiencing frequent respiratory illnesses.
4. The third hormone that is released from the adrenal gland (specifically the adrenal cortex) is called aldosterone. The purpose of this hormone is to increase blood volume, thus blood pressure. It makes sense that this would be beneficial in order to contend with whilst a stressor is present, however once the stressor has passed, there is evidence that prolonged stress overtime can lead to elevated blood pressure often diagnosed as ‘essential hypertension’. That said, longitudinal research examining this has recently reported a paradoxical effect whereby chronic stress can lead to clinical hypotension. That is, a prospective cohort study examining over 17,000 people over 22 years has found that anxiety and depression were associated with a decrease in blood pressure particularly when they experienced a persistent high symptom level (Hildrum, et al., 2011).
5. The pituitary also increases thyroid stimulating hormone (TSH) which stimulates the thyroid to increase thyroxin. Thyroxin essentially contributes to raising metabolism and as such, our breathing rate, heart rate, blood pressure and gut motility. As such, when thyroxin is high, it can affect the digestive system (contributing to IBS) and may also lead to panic attacks (often related to a medically diagnosed overactive thyroid).
All in all, stress is multi-modal, multi-faceted and has various ways in which it affects your physical and mental health. If you’re experiencing lots of demands, little recovery time, and/or feel overwhelmed you can rest assured your body is working hard in the background to help you manage and keep things in balance. Being in a stressful state or situation is a problem unless you don’t have sufficient resources or resilience to absorb it.
“It’s not stress that kills us, it’s our reaction to it’ ~ Hans Selye