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The Physiology of Stress


The General Adaptation Syndrome

It was 1936 and the Austrian researcher Hans Selye thought he had discovered a new hormone during one of his endocrinal experiments on animals. By injecting ovarian extracts into laboratory mice, he obtained specific reactions such has swelling of the adrenal cortex and the atrophy of organs that were important players of the immune system. He continued his experiments and injected substances extracted from other organs and he realized that the mice's bodies reacted in a similar way. Seyle believed he had discovered a new hormonal substance that induced specific reactions but he later realized that what he had actually discovered was the body's generic reaction to an external stimulus. It would later be named the General Adaptation Syndrome. The reactions represented the organism's adaptation process (stress) to a disturbing event (stressor).

Eustress: Adaptation that Allows for Survival

What Selye discovered was that our bodies react to a stressful event in a generic way (unspecific). This reaction or response represents a positive defense mechanism. It is an adaptation that allows the individual or the species to survive, a biological mechanism developed in ancient times in an environment that is very different from the one in which modern man lives today. The stress response in this case is not only a positive mechanism but also a necessary one and Seyle later called this eustress, healthful stress because it enhances function and results in positive feelings.

How Does Stress Manifest on a Physical Level

The etymology of the word stress comes from the Latin root strictus, to tighten, and in engineering terms indicates the state of metals that are exposed to extreme pressure.
An organism is exposed to pressure originating from the outside and to return to a “safe” situation, it triggers a series of internal events to recreate that state of calm.
So in the history of mankind (a period that is much much longer than that of written history) what could have been these stressful events and what was the adaptation response that compensated them? First off there were external physical events that created dangerous situations: predators, meteorological conditions, battles, hunting, etc. The adaptation mechanism was needed to create a rapid and efficient response – the more intense the situation, the more rapid the response. How does the mechanism work? It creates rapid blood flow towards the peripheral muscles (arms, legs, stabilizers) rather than towards internal organs. Constriction of the blood vessels occurs which in turn increases blood pressure and the rate at which blood flows, increasing also the heart rate. Pupils dilate. Blood flows away from the skin (the skin becomes clammy) in order to reduce blood loss in case of a wound. The muscular myofibrils enter into an alert state (muscle trembling). The breathing pattern changes in order to adapt to the increased amount of oxygen needed and the increased cardiac rate. At the same time, to generate energy, glucose is made available by breaking down the glycogen located in the muscles, opening up the adipocytes through hormones such as adrenaline. Finally even protein structures are broken down into simpler substances (catabolism), releasing energy and gluconeogenesis takes place (formation of glucose from a noncarbohydrate source such as proteins). It is for this reason that excessive stress leads to weight loss.

Any small variation in the surrounding environment leads to an immediate response on a behavioral level: a sudden sound makes a person react by jumping, running, striking out, defending oneself. An incredible concentration of energy brings the organism to a vigil state of alert that is otherwise impossible to achieve volontarily without a real stressor. This is why athletes reach their maximum performance during competitions, because the body interpretates the competition with the primordial instinct for survival.

Thus stress, or eustress, is a positive response, absolutely compatible with life and proportional to the body's ability for recovery. Its main characteristics are that the stress is intense but of short duration. The body in fact is not able to handle such an intense response for a long period of time. It is not by chance that the body's anaerobic metabolic mechanism can function for only less than a minute under such extreme pressure. Instead, extreme exertion lasting for a long period of time needs an aerobic metabolism which is more gradual and constant. And it is not by chance that the anaerobic metabolisms, those that are responsible for reacting to the need for an immediate and intense reponse (resulting in a lack of oxygen), are those that stimulate supercompensation, an adaptation that occurs in order to face stimuli that become progressively more intense.

This is the natural relationship between the stressor (the agent that disturbs the state of calm) and the stress (our bodies' physiological reaction that seeks to restore that calm).

There are also situations that are not dangerous that however also produce an adaptation response, such as the instinct for reproduction. In these cases the situation is perceived as a stress and is prone to subjectivity whereas an imminent physical danger is perceived more from an objective standpoint.

The Emotional Component and the Subjective Interpretation of the Stressful Event

The nervous system receptors catch the stimulus. Whether it is visual (a large object is about to fall, a ferocious animal is about to attack), tactile (a hot or sharp object), a sound or a scent, it sends a signal that travels through the network of nerves and reaches the central nervous system where signals are interpretated by the thalamus system and by the limbic system which assigns an emotion to the event. It then reaches the cerebral cortex and there it completes the cognitive perception of the event. In other words, the interpretation of an event is mediated by the emotions connected to it.

Distress: Negative and Persisting Stress

Individuals react differently when faced with a situation, in particular in those kind of situations where the stress factor is of low intensity and does not require an immediate response. We often find ourselves in situations that are seen as stressful due to our upbringing and culture, due to societal norms (e.g. scholastic performance, the fear of disappointing someone). These are events that cannot be considered dangerous but our personal upbringing may actually lead us to misinterpret these as danger. In such cases, our body gets mixed signals and our physiological response does not manifest completely. Part of it lingers in our system and with it the physiological adaptation mechanisms linger too. In the long run this state of stress becomes chronic and always remains somewhat past the limit of normality (high blood pressure, chronic inflammation, occasional cardiac dysrhythmia, etc.). This is what is called negative stress, distress – what modern man has acquired through his constant dealings with false dangers or better yet, with dangers that originate on a psychological level rather than a physical level.

Stress Induced by Association

An event which in itself is not stressful, such as the perception of an odor or a sound, could be associated with an alarming event and can trigger an adaptation response even when the event is not presented together with the danger that it is associated with.

In summary, the general adaptation syndrome is necessary in order to respond to situations that alter man's state of calm and to return to that state of calm and to the normal state of adaptation (eustress). In cases where a harmless event is misinterpretated as critical, the individual could face difficulties in resolving the issue and as a consequence, the state of stress may linger over time (distress). For example, an hour before an exam a student may be anxious, she may be feel flushed, her heartbeat may accelerate…and until she completes the exam this alteration will continue, creating an abnormal situation that is difficult for the body to handle. This perturbation may then manifest itself in a number of ways, such as a skin rash, hair loss, mood swing, a stomachache, loss of concentration, etc.

So the stress cycle begins with the first stage, the interpretation of an event (alarm), that leads to a reaction (resistance) and finishes with a return to normality that brings our body's functions back to its regular state (heart rate, blood flow, etc.) and above all calms the inflammatory state through cortisol.

What is important is the duration of all of this. Inflammation is useful if it lasts only for a brief period but if inflammation becomes chronic, then it can lead to any number of consequences.

Thus distress is mainly due to the duration of the stress and to its nature. Like in Selye's experiment, even foreign substances, and not necessarily an event, can create a stressful disturbance for the organism. In this case the reaction is strictly physiological since on a mental level the individual is not aware of the disturbance. And this is how food plays such an important role in our bodies' stress levels. An obvious example is the stress that caffeine induces on our bodies.
What we eat plays a fundamental role in helping to create the environment in which the adaptation response manifests. Substances that stimulate and excite will amplify the response. High blood pressure will put the organism at risk when the adaptation reaction peaks since there is less of a margin for increasing blood pressure as a response. Likewise when an individual has poor blood circulation due to a high level of lipids in the blood.
All of this is to point out that stress is a natural event but many of our modern habits have turned stress into a danger and even create stress when there is no real triggering factor.

Exercising is the Solution: Compensation and Eliminating Distress

As we have seen, psychological stress cannot be resolved by a physical response in the way that our bodies were designed to deal with physical stress. And as we have seen, the adaptation response is more efficient in a healthy individual. Thus one sure solution is to eliminate the stress through exercising while at the same time keeping ourselves fit.
The end solution is to remove the false stress factor and to fully come to terms with the event on a psychological level, but until this can be achieved, in the meantime to resolve the emergency situation, physical activity is definitely an excellent and natural way to “let loose”. When an individual faces a dangerous situation his organism prepares to escape, to jump, to strike back. If you cannot escape from an exam that you will take in an hour or from some other familiar problem, then channel your anxieties and nervousness into physical activity. Open up a new channel in the dam before it completely collapses.

Furthermore, together with exercising it is also wise to engage in some kind of meditative activity, something that allows you to distance yourself from thoughts related to the stressful situation. In this way you are allowing the adaptation mechanism to kick in (in fact, this decreases your heart rate, your need for oxygen, cerebral activity, muscular tension) and it may also help you to be more objective and to understand the situation for what it is and not what you have interpretated it to be through your emotions.

24/07/2008