病因

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 major groups:

• External (exogenous) conditions combine 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), routine disruptions (imbalance between work and active recreation), as well as the social environment generating frequent conflict situations and chronic stress.
• Internal (endogenous) conditions are intrinsic properties of the organism itself that determine its readiness to encounter a pathogen. These include baseline resistance to a specific factor, body build features (constitution), sex, age, and specifics of the type of higher nervous activity (HNA).

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, in modern pathology, the role of the organism's own state—its reactivity—increases colossally. This is as fundamental a quality of the living as growth, reproduction, heredity, or metabolism.

Reactivity represents a property of the integral organism (necessarily possessing a nervous system) to respond differentially 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. Conditionality of factor action directly depends on resistance. For example, during rapid ascent to high altitude, altitude sickness does not develop in 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 mycobacteria in the lungs without the clinical picture of tuberculosis.
3. Pathogenic action of indifferent factors manifests itself 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 hereditary fixation of crucial traits. It determines the features of a specific biological species. Classic examples: rabbits are completely unsusceptible 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 its species. Age reactivity explains why children, due to the immaturity of the immune system, are more susceptible to infectious diseases. Sex reactivity determines better tolerance to blood loss in young women and higher resistance to physical exertion in young men. Constitutional reactivity is based on stable morphofunctional and psychological features: for example, asthenics tolerate strong and prolonged loads significantly worse than normosthenics.
• 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

The fundamental conclusion of general pathophysiology states: the possibility of occurrence, course features, and outcomes of pathology are determined by the 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 for the further development of the disease is no longer required. Typical examples of such a mechanism: radiation sickness, frostbite, thermal burns, myocardial infarction, and tumor formation.
• Constant presence of the cause. The etiological factor not only triggers the disease but continues to act on the organism continuously throughout the entire period of the disease. This is characteristic of such conditions as ischemic heart disease (IHD), diabetes mellitus (DM), various symptomatic arterial hypertensions, and hyperthyroid states.

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该主题的其他拓展内容

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

“第 2 章：普通疾病学”的其他主题

本资料由 WhiteCoat Pro 讲师根据医学院校教学大纲编写。仅供教育参考。