Essence and forms of the adaptation process
Adaptation always proceeds in stages. The concept of this phenomenon was formulated by the outstanding pathologist Hans Selye. He emphasized that the entire body participates to one degree or another in any form of adaptation. There are two main forms:
- General (generalized, systemic) process. Characterized by a large-scale reorganization involving all or the absolute majority of physiological systems and organs.
- Local process. Observed locally in individual tissues or organs upon their injury (alteratio). Typical examples of local adaptation include reactions in local inflammation, allergy, tumor growth, or other types of damage.
Components of adaptation to emergency factors
When encountering a stress factor, the body triggers the combined activation of two types of reactions:
- Specific component. Provides targeted adjustment to the action of a particular stimulus. Examples include adaptation to hypoxia, severe cold, excessive physical exertion, shifts in homeostasis parameters, or substance imbalance.
- Non-specific component. Consists of general changes in vital activity that occur in response to any factor of unusual strength, duration, or character. It is this complex of universal reactions that is designated by the terms stress or stress reaction.
The result of the interaction of these two components is increased resistance and successful adaptation to changing living conditions.
Outcomes: optimal and pathological realization
Adaptation can end in different ways, depending on the intensity of the threat:
- Optimal realization. A state of high resistance is formed that the body did not previously possess. The ability to survive in conditions previously incompatible with life and to solve insoluble tasks appears. Here, cross-adaptation is clearly manifested — a phenomenon in which increased resistance to one factor is accompanied by enhanced protection against other stimuli.
- Pathological realization (adaptation syndrome as pathology). Occurs if the stress factor has a destructive intensity or acts for an excessively long time. In this case, the process of extreme adaptation is combined with profound disorders of vital activity, leading to the development of diseases or death.
Etiology: exogenous and endogenous causes
According to their origin, the causes of stress are divided into two groups. The most frequent triggers are exogenous agents:
- Physical: significant fluctuations in atmospheric pressure, temperature influences (up to adynamia), excessive physical activity, gravitational overloads.
- Chemical: deficiency or excess of oxygen in the inhaled air, starvation, fluid imbalance, intoxication with chemical substances.
- Biological: infection, poisoning with exogenous biologically active substances (BAS), acute and chronic diseases.
Endogenous causes include functional insufficiency of tissues and systems (due to injuries, intoxications, pathologies), as well as deficiency or excess of BAS effects (hormones, enzymes, cytokines, peptides).
Factors determining the development of the syndrome
Two factors are of paramount importance for the outcome of adaptation. First, this is the state of the body's reactivity, which determines the very possibility of the syndrome's occurrence and the features of its dynamics. Second, the specific conditions of action of extreme factors. External conditions can exacerbate the pathogenic effect (e.g., high humidity and wind multiply the effect of low temperature). Internal conditions are also critical: for example, insufficient activity of hepatic microsomal enzymes leads to the accumulation of toxic metabolic products, which creates a high risk of developing endotoxin shock.
Briefly: answers to topical questions
What stages of the general adaptation syndrome did Hans Selye identify?
In the development of the adaptation syndrome, by analogy with the stress reaction, three stages are distinguished:
- Alarm stage — already at this stage, the transport of energetic, metabolic, and plastic resources from unactivated tissues and organs to the dominant organs implementing specific adaptive reactions takes place.
- Resistance stage.
- Stage of exhaustion — an optional stage; develops upon repeated repetition of the adaptation process, cessation and subsequent resumption of the action of an extreme factor. Its pathogenesis is associated with the "exhaustion" of specific adaptation systems and a decrease in the capacity for energy and plastic provision.
What are the pathogenetic mechanisms of pathological adaptation and tissue damage during stress?
Pathological realization of adaptation develops if the stress factor has a high destructive intensity and/or excessive duration. An excessively pronounced or prolonged stage of alarm can cause the development of pathology.
Main confirmed mechanisms and damage factors:
- Hypercatecholaminemia.
- Excess of glucocorticoids and mineralocorticoids, thyroid hormones, and other biologically active substances.
- Ischemia of individual organs and tissues.
- Pathological vicious circles (circulus vitiosus) — form at the stage of insufficiency of adaptive mechanisms; the initial pathogenetic factor triggers a closed complex of escalating disorders that amplify the action of the initial factor via a positive feedback principle.
With prolonged exposure to a stressor and excessive activation of metabolism in tissues, dystrophic changes, hypotrophy, erosions, ulcers, and necrosis can develop.
What is the role of glucocorticoids and catecholamines in the nonspecific component of adaptation?
Glucocorticoids and catecholamines participate in the stress response and the body's adaptive and compensatory reactions.
Effects confirmed by sources:
- Glucocorticoids ensure the body's adaptation to chronic stress.
- Their action is associated with shifts in protein and carbohydrate metabolism.
- Cortisol increases tissue sensitivity to catecholamines, particularly adrenaline.
- Glucocorticoid secretion is stimulated by ACTH.
- Catecholamines of the adrenal medulla regulate cardiovascular activity and participate in the body's adaptive and compensatory reactions.
- During stress, excessive release of glucocorticoids can lead to excessive suppression of immune responses.
Class and exam questions
What is cross-adaptation?
This is a phenomenon whereby successful adaptation of the body to one extreme factor simultaneously increases its resistance to completely different stimuli.
What is the difference between specific and nonspecific components?
The specific component is responsible for protection against a specific threat (e.g., cold or hypoxia). The nonspecific component is a universal reaction (stress) triggered by any strong stimulus, regardless of its nature.
Can adaptation cause harm to the body?
Yes, if the stress factor acts for too long or has destructive power. In such cases, pathological adaptation develops, leading to illness or death.
What factors determine the severity of adaptation syndrome?
The primary role is played by the body's initial reactivity and concomitant conditions. For example, external conditions can enhance the pathogenic effect, while internal disorders can hinder the neutralization of toxins.
What else to study on this topic
- Mechanisms of local adaptation development in inflammation and tumor growth
- Pathogenesis of endotoxic shock against the background of hepatic enzyme deficiency
- The role of biologically active substances (cytokines, peptides) in the stress response
- The influence of exogenous physical and chemical factors on homeostasis parameters
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