Etiological factors

Exogenous and Endogenous Conditions

For an etiological factor to realize its pathogenic effect, certain conditions are necessary. By themselves, they are not capable of causing a disease, but they can significantly facilitate or, conversely, hinder its development. Traditionally, they are divided into two large groups:

• External (exogenous) conditions unite environmental factors. These include environmental problems (water and air pollution, exposure to industrial, agricultural, and domestic agents), nutritional disorders (quantitative deficiency or qualitative inadequacy of nutrition), schedule disruptions (imbalance between work and active rest), as well as the social environment generating frequent conflict situations and chronic stress.
• Internal (endogenous) conditions are the inherent properties of the organism itself that determine its readiness to encounter a pathogen. These include baseline resistance to a specific factor, constitutional features (body type), sex, age, and the specifics of the higher nervous activity (HNA) type.

Reactivity of the Organism and Its Significance

With the development of society and the advancement of medicine, the range of crude pathogenic factors is narrowing: the level of traumatism is decreasing, the number of severe poisonings is diminishing, and general living conditions are improving. Against this background, the role of the organism's own state—its reactivity—increases colossally in modern pathology. This is as fundamental a quality of living matter as growth, reproduction, heredity, or metabolism.

Reactivity represents a property of the integral organism (necessarily possessing a nervous system) to differentially respond to stimuli of the external and internal environment by altering its vital activity. The effect of encountering an etiological factor is not always linear:

1. Obligate pathogens (extreme temperatures, severe mechanical trauma, high doses of radiation) possess absolute aggressiveness and cause pathology in all people without exception.
2. The conditional nature of factor action directly depends on resistance. For example, upon rapid ascent to high altitude, mountain sickness develops far from everyone. Also widely known is the asymptomatic carriage of pathogenic microbes in the tonsils without the development of tonsillitis, or the presence of Koch's bacilli in the lungs without the clinical picture of tuberculosis.
3. Pathogenic action of indifferent factors manifests under altered reactivity. Completely ordinary odors or everyday food products (berries, chocolate, chicken eggs) are capable of provoking a disease (allergy).

Classification of Reactivity

Reactivity is not a homogeneous concept. Depending on biological properties, three main levels are distinguished:

• Species reactivity. It is formed in the process of long-term evolution through mutations, natural selection, and the hereditary fixation of crucial traits. It determines the characteristics of a specific biological species. Classical examples: rabbits are completely resistant to the causative agent of syphilis, and they do not develop atherosclerosis, unlike humans.
• Group reactivity. It depends on the individual's belonging to a certain category within their species. Age-related reactivity explains why children, due to the immaturity of the immune system, are more susceptible to infectious diseases. Sex-related reactivity determines better tolerance to blood loss in females and higher resistance to physical exertion in males. Constitutional reactivity is based on stable morphofunctional and psychological features: for example, asthenics tolerate strong and prolonged loads significantly worse than normostenics.
• Individual reactivity. It is formed on the basis of inherited information, individual variability, and the unique life experience of a specific organism. Unlike species and constitutional reactivity, it can be not only physiological, but also pathological.

Duration of Action of the Etiological Factor

A fundamental conclusion of general pathophysiology states that the possibility of occurrence, the features of the course, and the outcomes of pathology are determined by a combination of pathogen properties, organism reactivity, and environmental conditions. At the same time, the temporal nature of the interaction between the cause and the organism can proceed according to two different scenarios:

• Short-term action of the cause. The etiological factor acts exclusively as a starting trigger. It initiates the pathological process, after which its presence is no longer required for the further development of the disease. Typical examples of such a mechanism include radiation sickness, frostbite, thermal burns, myocardial infarction, and tumor formation.
• Continuous presence of the cause. The etiological factor not only triggers the disease, but also continues to act on the organism continuously throughout the entire period of the disease. This is characteristic of such conditions as coronary artery disease (CAD), diabetes mellitus (DM), various symptomatic arterial hypertensions, and hyperthyroid states.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of species reactivity formation in the process of evolution
• The influence of the higher nervous activity type on endogenous conditions
• Differences between physiological and pathological individual reactivity
• Constitutional reactivity: features of asthenics and normostenics
• The role of nutritional factors in reducing overall resistance

Other topics in "Chapter 2. GENERAL NOSOLOGY"

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