Diseases of the internal environment

Concept of health, norm, and environmental impact

The vital activity of the organism continuously oscillates between two interrelated forms: the state of health and the development of disease.

• Health in a biological context represents a person's ability to achieve full social and biological adaptation. It is a state in which the body is optimally adapted to constantly changing conditions of both the external and internal environment. The World Health Organization expands this concept, defining it as a state of complete physical, social, and spiritual well-being, and not merely the absence of visible physical defects or diagnosed diseases.
• Norm is a state of optimal functioning under strictly defined conditions of existence. It is important to understand that the concept of "norm" is much broader than the concept of "health." Although in clinical practice they are often used as synonyms, there are important discrepancies between them. A person can be clinically completely healthy, yet differ significantly from generally accepted population standards of the norm. These differences may concern body weight, height, general proportions, communication style, or intelligence level.

Pathological changes and internal environment disorders are often triggered by extreme external factors. Pathogenic impact is exerted not only by the appearance of foreign agents, but also by an excess, acute deficiency, or complete absence of those environmental components to which the biological species has adapted throughout phylogeny and individual ontogenesis. Extreme triggers include sharp fluctuations in atmospheric pressure, extremely high or low temperatures, radiation, as well as aggressive chemical and physical agents.

The success of resisting these factors depends on adaptation mechanisms (such as acclimatization), which make it possible to maintain vital functions under stress. The ability to adapt is strictly individual and relies on three main factors:

1. The genetic predisposition of the organism.
2. The current state of health.
3. The person's level of physical fitness.

Mechanisms of decompensation in hypothermia

One striking example of severe homeostasis disruption under the influence of extreme temperatures is hypothermia. The stage of decompensation develops with prolonged, continuous exposure to cold when all available adaptive responses of the organism are depleted.

Pathogenesis of decompensation:

• There is a critical decrease in temperature not only of the body's outer shell, but also of its "core" (internal organs, primarily the brain).
• Deep cooling of brain structures provokes a complete failure of central thermoregulation mechanisms.
• Progressive suppression of cortical and subsequently subcortical center activity is observed.
• Heat production processes become absolutely ineffective against the background of ongoing massive heat loss.

In this phase, the rectal temperature rapidly drops below the $35^\circ C$ mark and continues to fall. A fundamental destruction of homeostasis occurs: the organism loses the ability to independently maintain heat balance and becomes poikilothermic (now its internal temperature passively depends on the ambient temperature). Vicious cycles are formed that only potentiate the further development of hypothermia and exacerbate disorders of basic life processes.

The clinical and neurological picture is characterized by profound depression of central nervous system functions. The symptoms are particularly pronounced in childhood:

• Pronounced hypodynamia develops.
• The patient falls into a state of profound apathy.
• Pathological drowsiness increases.

The natural outcome of the exhaustion of all compensatory mechanisms is the development of coma (in clinical practice, this stage is sometimes distinguished separately as the stage of "hypothermic sleep" or deep coma).

Common pathogenesis of seizure states

Another classic example of pathologies closely related to the disruption of the constancy of the internal environment is seizure syndromes. Despite the extreme diversity of causes of seizures (pronounced polyetiology), the basic mechanism of their development always has a universal nature.

The foundation of the pathological process is a combined disorder of hemircirculation (blood flow) and the loss of internal environment constancy directly within the nervous system tissues. Local homeostasis disruption leads to neurons entering a state of critical hyperexcitability. As a result, a stable pathological hyperdischarge is formed in the nervous tissue, which is subsequently realized as a clinically pronounced seizure attack. Understanding this single mechanism is critically important for developing approaches to pathogenetic therapy.

Class and exam questions

What else to study on this topic

• Mechanisms of physiological and biochemical adaptation (acclimatization) to extreme conditions
• Compensation phases and vascular reactions in the early stages of overcooling
• The effect of atmospheric pressure changes on tissue homeostasis
• Principles of prevention and treatment of diseases associated with extreme factor exposure

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.