All about General Adaptation Syndrome

3 minutes

General adaptation syndrome is a bodily response to stress that has three stages.

Last update: 19 May, 2020

Hans Selye, professor and director of the Institute of Experimental Medicine and Surgery in Canada, introduced the concept of general adaptation syndrome (GAS) in 1950. He based it on various studies such as those by Claude Bernard, Frank Hartmann, and Cannon. This is because the scientist tried to establish a network of different concepts that could explain the stress response in humans.

Thus, Selye’s study considers stress not only a physiological process of adaptation but also a process that leads to disease.

The goal of the study was to search for new ovarian hormones. To do so, Hans injected a solution of extracts from cow ovaries into rats. As a result, he obtained an enlargement and hyperactivity of the cortex of the adrenal glands. In addition, some organs of the immune system (spleen, thymus, and lymph nodes) decreased in size. The solution also caused ulcers in the rats’ stomachs and intestines.

From this and other studies, Selye considered that there’s a pattern in the stress reaction. Thus, it stays the same regardless of the stimulus that’s causing it. As you can see, general adaptation syndrome integrates various closely related adaptive bodily reactions.

“Adaptability and resistance to stress are fundamental prerequisites for life and every vital organ participates in them.”
-Hans Selye-

The stages of general adaptation syndrome

General adaptation syndrome develops in three stages: the “alarm reaction”, the resistance stage, and the exhaustion stage.

The alarm stage

The onset of the hazard or threat occurs in this stage. Thus, the organism begins to develop a series of physiological and psychological alterations that predispose it to confront a given situation.

The sympathetic nervous system activates.
Physiological changes to “fight or flee” manifest.

The resistance stage

This is the adaptation stage to the stressful situation.
Firstly, physiological changes occur in the body to ensure the distribution of resources.
Then, the hypothalamic-pituitary-adrenal axis activates.
The body goes into energy-saving mode and sexual and reproductive activity decreases.
There’ll be consequences, such as a decrease in the general resistance of the organism, if there’s an adaptation. Also, a decrease in the performance of a person as well as less tolerance for frustration, among others.

The exhaustion stage

In this stage, there’s a loss of body resistance, and adaptation capacity takes place.
Diseases such as gastrointestinal ulcers, hypertension, myocardial infarctions, and nerve disorders can occur due to a lack of adaptation.
At this stage, physiological, psychological, or psychosocial disorders tend to be either chronic or irreversible.

General adaptation syndrome and allostasis

To adapt, the body sets adaptation processes in motion to counteract stressful situations. Thus, the goal of allostasis is to allow the body to reach homeostasis or a return to balance.

Homeostasis is the stability of the physiological systems that support life. These are coordinated physiological processes that operate to keep most states of the body constant. Walter Cannon defined this concept in the early 20th century. Also, he stressed the importance of activating the sympathetic nervous system.

One could define the allostatic load as the cumulative wear that occurs in different systems after a prolonged or poorly regulated response. Thus, this is the price the body pays when forced to adapt to adverse circumstances, both psychosocial and physical.

Types of allostasis

Repetition.
Lack of adaptation and habituation.
Prolonged response due to delayed recovery.
Inadequate response due to compensatory hyperactivity of other mediators.

Allostasis compensates for various problems, such as heart, kidney, and liver failure.

Thus, Sterling (2004) proposes that six interrelated principles are behind allostasis:

Organisms are designed to be efficient.
Efficiency requires reciprocal exchanges.
It also requires to be able to predict future needs.
Such prediction requires each sensor to adapt to the expected input range.
The prediction also requires that each effector adapt its production to the expected range of demand.
Predictive regulation depends on behavior, while neural mechanisms can also adapt.

Thus, general adaptation syndrome is an example of how stress is the origin of certain pathologies. Many stressful stimuli can cause this syndrome in your daily life, which is why it’s important to know about their existence and occurrence.