An individual who is awakened in the middle of the night by the discovery that their house is on fire is experiencing the alarm reaction stage of the General Adaptation Syndrome.

Example of General Adaptation Syndrome Alarm Reaction: House Fire

A person is hiking in the woods and suddenly comes face-to-face with a large bear. In the first few moments after seeing the bear, which of the following physiological responses would be most characteristic of the body's immediate reaction to this perceived threat?

The alarm reaction is the initial stage of the General Adaptation Syndrome, representing the body's immediate physiological response to a perceived threat. This phase is characterized by the activation of the sympathetic nervous system, which triggers the release of adrenaline from the adrenal glands. This hormonal surge initiates the fight-or-flight response, leading to physiological changes like an accelerated heart rate and increased respiration. Concurrently, the hypothalamic-pituitary-adrenal (HPA) axis also becomes active to help manage the stressor.

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Developed by endocrinologist Hans Selye, the General Adaptation Syndrome (GAS) describes the body's consistent physiological reactions to stress. The theory posits that this response occurs in three stages, regardless of the specific stressor: the alarm reaction, where initial fight-or-flight reactions begin; the resistance stage, where the body adapts to continuing stress; and the exhaustion stage, where the body's adaptive energy is depleted and stress begins to take a physical toll.

The General Adaptation Syndrome Theory

The fight-or-flight response, first identified by Walter Cannon, is the body's primary physiological reaction to a perceived threat. This response involves the coordinated activity of both the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. This built-in adaptive mechanism prepares an individual to either confront or escape a danger, thereby increasing the chances of survival by helping to maintain homeostasis.

Fight or Flight Response

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

The resistance stage occurs when exposure to a stressor is prolonged. In this phase, the body has adapted to the stressor and the initial shock of the alarm reaction has subsided. However, the body remains on high alert, prepared to respond to the stressor, though with less intensity than during the alarm stage.

General Adaption Syndrome: Resistance Stage

In his foundational research on stress, Hans Selye identified a distinct trio of physiological changes in rats subjected to prolonged stressors. These observable signs consisted of adrenal gland enlargement, shrinkage of the thymus and lymph nodes, and the formation of stomach ulcerations.

Physiological Signs of Prolonged Stress in Selye's Rat Studies

A central principle of Hans Selye's General Adaptation Syndrome is that the body's physiological response to stress is nonspecific. This means that the same pattern of coordinated reactions is triggered regardless of the particular type of stressor. For instance, the body reacts similarly whether the stress comes from extreme cold, physical injury, or excessive muscular exercise.

Nonspecificity of the General Adaptation Syndrome

General Adaptation Syndrome: Alarm Reaction

The General Adaptation Syndrome is often illustrated with a graph that plots stress resistance against time. The horizontal x-axis represents the duration of exposure to a stressor, while the vertical y-axis represents the level of stress resistance. The curve on the graph demonstrates the progression through the three stages: an initial dip during the alarm reaction, a sustained high level during resistance, and a final decline into exhaustion, showing that prolonged stress eventually depletes the body's ability to cope.

Graphical Representation of the General Adaptation Syndrome

The exhaustion stage is the final phase of the General Adaptation Syndrome, occurring when exposure to a stressor is prolonged. In this stage, the body's capacity to adapt is depleted, and its resistance to stress is exhausted due to the cumulative physical wear on its tissues and organs. This depletion can lead to severe health consequences, including illness, disease, permanent physical damage, and potentially death.

General Adaptation Syndrome: Exhaustion Stage

Despite its limitations, Hans Selye's General Adaptation Syndrome model has had a significant influence on the field of stress. Its primary contribution is providing a general framework that explains the mechanism by which stress can cause physical damage and lead to disease.

Impact of the General Adaptation Syndrome Theory

Prolonged or repeated exposure to stressors, as conceptualized by the General Adaptation Syndrome, has been implicated as a contributing factor in the development of several serious health disorders. Specific conditions linked to this type of chronic stress include hypertension and coronary artery disease.

Link Between Prolonged Stress and Disease

A primary limitation of the General Adaptation Syndrome model is its conceptualization as a purely response-based theory of stress. It concentrates exclusively on the body's physiological reactions and largely overlooks the role of psychological factors, such as an individual's cognitive appraisal and interpretation of threatening situations.

Shortcomings of the General Adaptation Syndrome Theory

The endocrine system is a network of glands responsible for secreting hormones that regulate normal bodily functions.

Endocrine System

Homeostasis is the process by which a biological system maintains a stable, balanced internal environment to ensure optimal functioning. This state of equilibrium involves stabilizing key physiological variables, such as blood pressure, respiration, digestion, and body temperature, at levels ideal for survival.

Homeostasis

The sympathetic and parasympathetic systems operate with complementary functions, working together in tandem to maintain the body's homeostasis, which is a state of internal equilibrium where biological conditions are kept at optimal levels.

The Sympathetic and Parasympathetic Nervous Systems' Role in Homeostasis

In contemporary society, the fight or flight response is frequently activated by psychological stressors, such as public speaking or academic exams, rather than the physical threats it evolved to handle. Although no real physical danger is present in these situations, the body still initiates this physiological response to a perceived threat, making the response less adaptive in a modern context.

Modern Triggers for the Fight or Flight Response

The fight or flight response, while evolutionarily adaptive for acute physical threats, can be detrimental to health when persistently activated by modern psychological stressors. Since these threats often cannot be resolved by fighting or fleeing, the body experiences prolonged stress, which can lead to negative health outcomes. Research has linked this chronic exposure to an increased susceptibility to heart disease and impaired functioning of the immune system.

Health Consequences of Chronic Activation of the Fight or Flight Response

After a perceived threat has been resolved, the parasympathetic nervous system becomes active, initiating restorative processes that return the body to a relaxed state of equilibrium, often called the 'rest-and-digest' response. This system counteracts the fight-or-flight response by normalizing bodily functions. For example, it causes heart rate and blood pressure to decrease to normal levels, pupils to constrict, and bladder control to be restored. Additionally, it promotes energy conservation by stimulating the liver to store glucose in the form of glycogen for future use.

Parasympathetic Nervous System

An example illustrating the evolutionary advantage of the fight or flight response involves an early ancestor, out hunting small game, who suddenly disturbs a large bear with her cubs. This perceived threat triggers immediate sympathetic activation, leading to a cascade of physiological changes: pupils dilate, heart rate and blood pressure increase, the bladder relaxes, glucose is released from the liver, and an adrenaline surge occurs in the bloodstream. These adaptations provide the energy reserves and heightened sensory capacity needed to either fight off the threat or run away to safety.

Example of Fight or Flight Response: Encountering a Bear

Activation of the fight-or-flight response, prompted by a surge of epinephrine and norepinephrine, initiates a cascade of physiological adjustments to prepare the body for a threat. These changes include:
* Pupil dilation
* Increased heart rate and blood pressure
* Heavy breathing and dilation of bronchi
* Perspiration
* Muscle tension
* Inhibition of digestion (causing sensations like 'butterflies in the stomach') and salivation
* Stimulation of glucose breakdown and release from the liver
* Relaxation of the bladder

Physiological Changes During the Fight-or-Flight Response

The Hypothalamic-Pituitary-Adrenal (HPA) axis is a crucial neuroendocrine system that orchestrates the body's response to stress. While highly active during a stress response, its hormonal cascade operates more slowly than the immediate reaction of the sympathetic nervous system. The process begins when the hypothalamus releases corticotropin-releasing factor (CRF), which signals the pituitary gland to secrete adrenocorticotropic hormone (ACTH). ACTH then travels to the adrenal glands, stimulating them to release hormones like cortisol into the bloodstream. This hormonal sequence ultimately provides the body with the energy needed to manage the stressor.

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