Essence and Forms of the Adaptation Process
Adaptation always proceeds in stages. The concept of this phenomenon was formulated by the prominent pathologist Hans Selye. He emphasized that in any form of adaptation, the entire body participates to one degree or another. 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, allergies, tumor growth, or other types of damage.
Components of Adaptation to Extreme 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 nature. It is this complex of universal reactions that is designated by the terms stress or stress response.
The result of the interaction between these two components is an increase in resistance and successful adjustment to changing living conditions.
Outcomes: Optimal and Pathological Realization
Adaptation can conclude 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 emerges to survive in conditions previously incompatible with life and to solve insurmountable tasks. This clearly demonstrates cross-adaptation—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 destructive intensity or acts for an excessively long time. In this case, the extreme adaptation process combines with profound disturbances in 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 effects (up to adynamia), excessive physical activity, gravitational overloads.
- Chemical: deficiency or excess of oxygen in inhaled air, starvation, fluid imbalance, intoxication with chemical substances.
- Biological: infection, poisoning by exogenous biologically active substances (BAS), acute and chronic diseases.
Endogenous causes include functional insufficiency of tissues and systems (resulting from trauma, intoxications, pathologies), as well as a deficiency or excess of BAS effects (hormones, enzymes, cytokines, peptides).
Factors Determining the Development of the Syndrome
Of greatest importance for the outcome of adaptation are two factors. First 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 are the specific conditions under which extreme factors act. External conditions can aggravate the pathogenic effect (for example, high humidity and wind repeatedly amplify the effect of low temperature). Internal conditions are also critical: for example, insufficient activity of liver microsomal enzymes leads to the accumulation of toxic metabolic products, creating a high risk of endotoxic shock.