There are three types of theoretical models that attempt to explain stress , depending on whether they consider stress as a response, as a stimulus or as an interaction between the stimulus and the response.

Here we will look at a response-based model, the Selye General Adaptation Syndrome . Selye’s model considers stress as a dependent variable, and configures its theory considering stress as an organism’s response. We will know it in detail in this article.

Hans Selye: stress as an answer

Hans Selye was an Austro-Hungarian physiologist and physician , born in Vienna in 1907, who developed a theory to explain the General Adaptation Syndrome (GAS). Selye defined stress as a general, stereotyped response involving the activation of the hypothalamic-pituitary-adrenal (HHS) axis and the Autonomous Nervous System (ANS).

According to the author, the body is activated by a source of stress. If the activation persists, the “Stress Syndrome” or General Adaptation Syndrome will appear.

The appearance of GAS leads to different changes at the physiological level. Three of the most important are:

  • Hyperplasia of the adrenal cortex (abnormal increase in its size).
  • Involution of the thymus (reduction in size and weight).
  • Development of peptic ulcer (open sores that develop on the inner lining of the stomach and upper intestine)

What is General Adjustment Syndrome?

Selye operationally defined stress by basing this definition on 2 objectifiable phenomena:

1. Stressor

Is all that demand that exceeds the resources of the individual and that evokes the pattern of stress response or General Adaptation Syndrome.

2. Stress response

It’s the General Adaptation Syndrome itself. Its appearance implies a series of changes that are produced as a consequence of the sustained presence of a stressor. Moreover, this activation response is both generalised (affects the whole organism) and non-specific (appears in any situation of stress).

Development phases

On the other hand, Selye differentiates three phases of the General Adaptation Syndrome:

1. Alarm phase

At a physiological level, two systems are activated in this phase : the neural and the neuroendocrine . This phase appears immediately after the threat. Different hormones are released: adrenaline, corticotropin and corticoids, aimed at mobilizing resources.

This phase, in turn, is divided into two sub-phases:

1.1. Shock phase

It is the most immediate reaction, and involves tachycardia, hypotonia, lowering of temperature and blood pressure.

1.2. Counter-shock phase

This is a rebound reaction, involving enlargement of the adrenal cortex and involution of the thymus. Signs opposite to the shock phase appear.

In the alarm phase, two things can happen: either the situation is overcome or it is not . If it is overcome, the General Adaptation Syndrome ends; if it is not overcome, the resources mobilised are reduced and the second phase appears: the resistance phase.

2. Resistance phase

Here the activation of the organism is high, although lower than in the previous phase. This activation can be maintained longer, as the organism, in a certain way, adapts to the stress.

The negative (physiological) symptoms here improve, and even disappear. The resistance shown by the person is higher for the noxious agent and lower for other stimuli than this one.

Again, two things can happen here: that the situation is overcome or that it is not. If it is overcome, the General Adaptation Syndrome ends, and if it is not overcome, the third and final phase arrives: the exhaustion phase.

3. Exhaustion phase

At this stage resources are exhausted. The individual loses the capacity to adapt to the stress , which is usually severe and prolonged. The symptoms of the alarm phase reappear.

This is when the individual is most vulnerable to disease. Furthermore, this phase is not irreversible, except in extreme cases, and the person will need a rest period to recover reserves.

Selye’s experiments

If we go to the origin of the General Adaptation Syndrome, we find the experiments developed by Hans Selye. These were aimed at discovering a new sex hormone. To do this, he injected ovarian extract into rats and analyzed the results, which allowed him to observe a constancy in the changes produced.

These changes included hypertrophy of the adrenal cortex, atrophy of the endothelial reticulum system, and the appearance of gastric and duodenal ulcers. Furthermore, the magnitude of such changes was proportional to the amount of ovarian extract injected .

Selye introduced different substances to the rats, and they all produced the same effect.

A few years later, when he was training as a doctor at the University of Prague, he had his first contact with patients. He found that many of them complained of general symptoms such as fever, headache, weight loss … and that these symptoms were independent of the illness they had.

The term stress

Thus, Selye called this effect “Sick Only Syndrome,” and related the concept to findings found in rats, which also reacted the same way to different substances.

Years later, Selye defined the condition under which the organism responds to harmful agents (stressors) with the term stress (meaning tension, pressure, coercion).

The concept of stress was quickly embraced and used worldwide , with its relevant adaptations.

Bibliographic references:

  • Bértola, D. (2010). Hans Selye and his stressed rats. University Medicine, 12(47), 142-143
  • Friend, I. (2012). Manual of Health Psychology. Madrid: Pirámide.