Starting and primary links of disease development
Any pathological process has a clear developmental structure. It is always underpinned by the starting (initial or trigger) link. This element is present in absolutely any form of pathology and largely determines its specific features. The characteristic of the trigger factor is that it may act throughout the entire period of the disease or operate only once—exclusively to launch the cascade of reactions, after which its influence ceases.
However, the central role in the development of the disease is played by the main (primary, leading) link of pathogenesis. This is a key, organizing element that usually exists from the very beginning until the complete termination of the pathological process. The physician's attention must be directed precisely toward the main link, as identifying it is critically necessary for conducting effective pathogenetic therapy.
Let us consider classical examples of main links in various conditions:
- In inflammation, the leading mechanism is the generation of inflammatory mediators and the realization of their effects in tissues.
- In anemias, the key link determining the severity of the condition is hypoxia.
- In allergic diseases, the basis of the process is the production and action of allergy mediators, specific antibodies (Abs), and the activity of sensitized lymphocytes.
Pathogenesis as a branched chain process
Pathogenesis is never an isolated phenomenon. It is always a dynamic process where a trigger factor initiates a complex, branched chain of interdependent reactions. One disorder inevitably pulls others along, forming a large-scale cascade of disturbances.
Diabetes mellitus (DM) serves as an excellent model for demonstrating this chain deployment:
- The leading factor is absolute or relative hypoinsulinemia (deficiency of the insulin hormone itself or its physiological effects).
- This deficiency leads to impaired glucose transport into cells.
- Cellular starvation causes severe disorders of energy supply, failures in transmembrane ion transport, damage to cell membranes, and a sharp decrease in the activity of enzyme systems.
- At the tissue level, this manifests as a disruption of plastic processes and dysfunction of organs and tissues.
- In the finale, an extensive cascade of other secondary disorders forms, affecting the entire organism.
Formation of a vicious circle (Circulus vitiosus)
A special and extremely dangerous phenomenon in pathophysiology is the formation of vicious circles, or in Latin, Circulus vitiosus. The essence of this phenomenon is that one of the links of pathogenesis becomes the direct cause of new disorders, which, in turn, support or potently potentiate (intensify) the action of this very same initial link. The process loops back onto itself.
A striking example of the formation of a Circulus vitiosus is the development of heat stroke:
- Initially, a significant increase in body temperature occurs.
- Against the background of hyperthermia, neuromuscular excitability naturally increases.
- Increased excitability leads to the development of pronounced seizures.
- Intense muscle contractions cause an increase in contractile thermogenesis (heat production by muscles).
- This additional heat leads to a further increase in body temperature. The circle is closed.
Interaction of mechanisms
It is important to understand that in the pathogenesis of various forms of pathology, only isolated pathways never work alone. The development of a disease is always a complex interaction. Both specific mechanisms, which determine the unique picture of a particular disease, and non-specific links, characteristic of the body's response to injury as a whole, participate inextricably in a single process.
Briefly: answers to topical questions
What are the examples of vicious circles in heart failure?
In heart failure, such mechanisms are directly confirmed in the literature:
- Anemia–heart–kidneys in CKD: impaired erythropoietin production in the kidneys is the main cause of anemia in chronic kidney disease; anemia causes a compensatory increase in the load on the heart due to tachycardia and increased stroke volume; further, renal vasoconstriction and fluid retention develop, followed by congestive heart failure. As a result, heart failure, kidney disease, and anemia mutually exacerbate each other's course.
- Sympathoadrenal mechanism in the progression of heart failure: reduced blood supply to the heart and the progression of its failure trigger the activation of the sympathoadrenal system; this leads to tachycardia and peripheral vasoconstriction. Peripheral vasoconstriction increases peripheral vascular resistance, resulting in an increased afterload on the heart.
What vicious circles form in shock states (e.g., in blood loss)?
In shock and extreme conditions, the literature cites the following vicious circles:
- Redistribution of blood flow: pooling of blood in dilated vessels of the abdominal cavity, lungs, and subcutaneous tissue → decreased circulating blood volume (CBV) → decreased blood flow to the heart (venous return) → decreased cardiac output → an even greater decrease in CBV and worsening of the condition.
- Microcirculatory-metabolic vicious circle in shock: hemodynamic disorders lead to altered microcirculation, impaired capillary perfusion, hypoxia, and metabolic disorders; circulatory tissue hypoxia leads to anaerobic glycolysis, lactate accumulation, and metabolic acidosis. Acidosis and vasoactive metabolites exacerbate microvascular paresis and promote the formation of sludges and microthrombi, closing the microcirculation vicious circle.
- Multiorgan vicious circle in traumatic shock: hemodynamic disorders in the liver can lead to total liver failure; hemodynamic disorders in the gastrointestinal tract lead to impaired GI functions and the development of intestinal autoinfection and autointoxication. Combined, these disorders potentiate each other, suppressing vital activity and leading to death without medical assistance.
- Hemorrhage–coagulopathy in combined pelvic trauma and TBI: pelvic bone fracture with hemorrhage → coagulopathy → worsening of TBI with the development of secondary hemorrhage and progression of hemorrhagic contusion foci.
- Lipoperoxide mechanism in extreme conditions: hypoxia developing in all types of extreme conditions is accompanied by the suppression of antioxidant defense and the intensification of free radical generation and lipid peroxidation.
For rapid analysis of pathogenesis, use the rule of three questions: 1. What triggered it? (Looking for the starting link—it sets the specificity). 2. What maintains it? (Looking for the main link—this is the target for therapy). 3. What aggravates it? (Looking for the vicious circle—the consequence that intensifies its own cause).
Class and exam questions
What is the difference between the starting link and the main link of pathogenesis?
The starting (trigger) link initiates the disease and determines its specifics, but may disappear in the process. The main link is the organizing basis of the pathology, which exists from start to finish and is the main target for treatment.
Why does a physician need to identify the primary link of pathogenesis?
Identifying the leading link is critically important for prescribing effective pathogenetic therapy. By eliminating the key mechanism (e.g., hypoxia in anemia), one can stop the development of the entire cascade of disorders.
How does a vicious cycle work using heat stroke as an example?
Elevated temperature causes seizures due to increased neuromuscular excitability. Seizures enhance heat production by muscles (contractile thermogenesis), which leads to an even greater rise in temperature and the closure of the circle.
What else to study on this topic
- The role of inflammatory mediators as the main link of pathogenesis
- Mechanisms of hypoxia development in various types of anemias
- Pathogenesis of allergy: from antibodies to sensitized lymphocytes
- Cascade of metabolic disorders in insulin deficiency
- Interaction of specific and non-specific mechanisms of disease
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