Stress: An evolutionary balancing act!

balancing act

Stress, is it a modern day concept or an age old foe? Every living being on this planet has experienced stress at some point in their life.  It’s not rare to hear of a person ‘feeling stressed’ or needing to ‘take some time out and recharge their batteries’ (as if they were the Duracell rabbit!). Stress is now accepted as part and parcel of modern life and being stress-free implies you’re a modern day yogi; to which we say namaste! As Darwin points out, our future as individuals and as a species depends on our ability to adapt to potential stressors (i.e. sources of stress; could be abstract or physical) and survive. So, what is stress? Googling the word gives rise to numerous links and images, the majority of which possess a negative connotation. But is stress something inherently bad?

The UK mental health charity Mind, states that stress doesn’t have a strict medical definition. A lack of set parameters defining what counts as stress and its innate subjectivity, presents us with a rather ambiguous issue, with no fixed solution. Stress, as we understand it, is a state of being; wherein the body copes with changes to normal physiological and mental well being.

The cells, organs and organ systems in our body are habituated to function optimally in a model internal environment. Naturally, they are designed to rectify any undesirable change to this environment, restoring balance. This balance or the ‘normal/relaxed’ state of the body is termed as homeostasis which is diligently maintained by different regulatory processes. Evolution has adequately equipped us to deal with change, assisting survival via adaptation. For instance, consider being attacked by a wild animal or in a slightly relatable case, being ‘attacked’ by an overbearing, horrible boss. Instinct leads us to react in one of two ways; – A) Fight: confront the threat/stressor (standing up for yourself!) or B) Flight: Run away from the threat/stressor (quitting!).

The question arises, what are the biological response mechanisms to stress? Hans Selye, a Hungarian endocrinologist, proposed three stages of the well-known fight or flight stress responses. According to Selye, stage 1 comprises of alarm bells, signalling the impending threat and prompting immediate response (in a bid to regain a state of homeostasis). During stage 2, stress responses bring about changes in physiology to further adapt to the continual stressor(s) and sustain. Finally, if the stress signals persist, the body is faced with stage 3 or exhaustion. This occurs when responses no longer elicit any change and the tired body cannot deal with the stressor anymore; resulting in damage, disease and eventually death.  Safe to say stress carries along with it a host of physical, behavioural and emotional symptoms which can affect a person’s daily life in various ways.

Stress responses are governed by two nervous complexities; the sympathetic-adrenal-medullary axis (SAM), playing a greater role in acute stress and the hypothalamic-pituitary-adrenal axis (HPA) which is more active during chronic stress.

One thing we experience without fail when faced with danger, is an instant rush of adrenaline. Picture this, you’re facing your ex or a car heading straight in your direction. In both cases, your heart rate shoots up, you feel warm, flushed and extremely alert. You may even freeze to your spot for a couple of seconds while your brain assesses the situation and comes up with an escape plan. But why does this happen?

Your body responds in this way because the sympathetic nervous system (SNS) is kicking into action. The SNS is the part of our peripheral, autonomic nervous system responsible for regulating unconscious, active and vital processes in our body (such as respiration, blood circulation, digestion etc.). It activates the adrenal glands (specifically the adrenal medulla) coaxing release of adrenaline (aka epinephrine) into the bloodstream. Preganglionic neurons emerging from the spinal cord, synapse onto cells in the adrenal medulla where the neurotransmitter, acetylcholine binds to the relevant receptors stimulating adrenaline release. This has widespread effects on different physiological systems, e.g. cardiovascular and respiratory systems which function more effectively. Skeletal muscles are increasingly perfused as blood flow is diverted away from relatively less essential processes or sites of trauma preventing blood loss. In essence your body is functioning optimally so you can either knock someone out or get the hell out of there!

Simultaneously, the hypothalamus in the limbic system of our brain stimulates the pituitary ‘master’ gland to release corticotrophin releasing hormone (CRH) in the blood. In turn, CRH excites the adrenal glands (this time, the adrenal cortex) to release the stress hormonecortisol’ in the blood stream. This works in tandem with adrenaline by aiding breakdown of stored energy reserves rendering them readily available, especially for the skeletal muscles. Moreover, the immune system deploys fighter immune cells and chemicals upon activation, which are stationed as first line, ready for defence. Increased blood and energy supply to the brain also enhances memory formation (to avoid a similar situation in the future) and decision making ability while keeping us alert and focused. These adaptive responses (comprising of adrenaline, cortisol and other chemical messengers) striving to maintain homeostasis are comprehensively referred to as allostasis. So surely stress is a good thing since it helps us assess and deal with the issue at hand, just like the anxious rush, we experience prior to a submission deadline/exam that helps us concentrate better.

It is obvious that all these changes are better suited in the short term, as rapid response against a stressor. Ideally, these secretions negatively feedback into their respective facilitatory systems to prevent further release and effect. However, imagine allostasis persisting for a longer period of time causing you to feel stressed out. Constantly being on guard (fight or flight) is bound to end up in fatigue and eventually, the need to replenish the spent energy will arise.

Constant elevation of blood pressure often results in atherosclerotic plaque deposition along walls of blood vessels. This exacerbates existing conditions and perpetually strains the heart, increasing the risk of stroke. In addition, chronic presence of cortisol and sugar (glucose) in the bloodstream gradually results in insulin resistance (diabetes) and hinders storage of glucose. This resulting wear and tear due to chronic stress and overactive allostatic mechanisms is termed allostatic load or overload. This may be the ‘bad and undesirable’ stress we tend to experience in daily life.

So, the effects of biological mediators of stress responses could be both protective and damaging to our body. Somehow, our modern lifestyles contribute towards a build-up of allostatic overload, culminating in pathology and a wide range of diseases. So could the detrimental effects of stress be managed by improving the efficiency of allostasis? Stress is such a prevalent motif and major concern in present day life that its efficient management is crucial (or you risk going entirely barmy!). Can we hijack the body’s stress responses and turn bad stress into good?

References:

  • Juster,R.P., McEwen, B.S. & Lupien, S.J., 2010. Allostatic load biomarkers of chronic stress and impact on health and cognition. Neuroscience and Biobehavioral Reviews, 35(1), pp. 2-16.
  • McEwen, B.S., 2004. Stressed or stressed out: what is the difference? Journal of Psychiatry and Neuroscience, 30(5), pp. 315-319.
  • Schneiderman,N., Ironson, G. & Siegel, S.D., 2005. Stress and health: psychological, behavioral, and biological determinants. Annual review of clinical psychology, 1(Lacey 1967), pp. 607-28.
  • Stratakis, C.a. & Chrousos, G.P., 1995. Neuroendocrinology and pathophysiology of the stress system. In Annals of the New York Academy of Sciences. Pp. 1-18.
  • Tsigos, C. & Chrousos, G.P., 2002. Hypothalamic-pituitary-adrenal axis, neuroendocrine factors and stress. In Journal of Psychosomatic Research. Pp. 865-871.
  • Vyas,A. et al., 2002. Chronic stress induces contrasting patterns of dendritic remodelling in hippocampal and amygdaloid neurons. The Journal of neuroscience: the official journal of the Society for Neuroscience, 22(15), pp.6810-6818.
  • http://www.mind.org.uk/information-support/tips-for-everyday-living/stress/#.V4qYRzVdysg

 

 

 

 

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