Classification and endogenous causes
According to their origin (etiology), all hyperthermic reactions are divided into three large groups: endogenous, exogenous, and combined. Endogenous disorders develop under the influence of internal factors and are subdivided into several types:
- Psychogenic. They occur against the background of significant psycho-emotional stress. Classic examples include stress reactions in students during exams or when solving life-critical problems. They also accompany mental disorders (e.g., hysteria) and various neurotic states. The main development mechanism is the powerful activation of the sympathoadrenal system.
- Endocrine. Based on the activation of exothermic metabolic processes. The most frequent causes are hyperproduction of catecholamines (observed in pheochromocytoma) and excess thyroid hormones (in hyperthyroid states). An important role here is played by the formation of specific substances — uncouplers of cellular oxidation and phosphorylation processes.
Neurogenic hyperthermic reactions
Neurogenic disorders belong to the endogenous group and are structurally divided into centrogenic and reflexogenic.
- Centrogenic. They develop upon direct irritation of the neurons of the central thermoregulation center (primarily the section responsible for heat production), as well as associated areas of the cerebral cortex and brainstem. Etiological factors include hemorrhages, mechanical trauma, growing tumors, and aneurysms in these areas. The leading mechanism involves sequential activation of hypothalamic neurons, the sympathetic nervous system, neurosecretory cells (synthesizing thyrotropin-releasing hormone), and adenohypophysial cells producing thyroid-stimulating hormone (TSH).
- Reflexogenic. They occur in response to strong, typically painful irritation of various organs and tissues. The main cause is exposure to reflexogenic zones. This happens during irritation of the hepatic bile ducts, renal pelvicalyceal system, and urinary tract (e.g., during stone passage). Endoscopic manipulations also serve as triggers: gastroscopy, colonoscopy, laparoscopy, and cystoscopy. The pathogenesis is driven by activation of the sympathoadrenal and thyroid systems, leading to intensified metabolism and increased heat generation.
Exogenous hyperthermic reactions
Exogenous reactions are provoked by environmental factors and are subdivided into drug-induced and non-drug-induced.
- Drug-induced. They occur upon administration of medications with adverse thermogenic effects. The main groups of such drugs include catecholamine-based agents, caffeine, ephedrine, L-DOPA, and thyroid hormones. In addition, reactions are caused by uncouplers of oxidation and phosphorylation containing calcium ions, non-esterified fatty acids (NEFA), and oligomycin.
- Non-drug-induced. Caused by chemical substances with pronounced thermogenic action. Etiology includes research purposes (animal experiments), accidental toxin ingestion, or occupational safety violations. Examples of such substances include 2,4-dinitrophenol, cyanides, and amobarbital. Their mechanism of action consists in the activation of the sympathoadrenal and thyroid systems followed by the uncoupling of tissue respiration processes.
Briefly: answers to topical questions
What stages are distinguished in the pathogenesis of a hyperthermic reaction (hyperthermia)?
Two main stages are distinguished in the pathogenesis of hyperthermia:
- Compensation stage — the adaptation stage.
- Decompensation stage — maladaptation of thermoregulation mechanisms.
- Hyperthermic coma — the final stage, which is sometimes singled out.
For the hyperthermic reaction, sources indicate: a temporary increase in body temperature above the norm due to the transient predominance of heat production over heat loss; thermoregulation mechanisms are preserved.
How does a hyperthermic reaction fundamentally differ from fever in terms of the setpoint mechanism?
The fundamental difference according to sources lies in the mechanism of temperature elevation.
| Criterion | Fever | Hyperthermic reaction |
|---|---|---|
| Mechanism | Temporary dynamic restructuring of the thermoregulation system with a shift of the "setpoint" to a higher level | Temporary increase in body temperature above the norm due to the transient predominance of heat production over heat loss; thermoregulation mechanisms are preserved |
The formulation regarding the "breakdown of the thermoregulation mechanism itself" for hyperthermic reaction is not supported by sources.
To quickly recall the types of endogenous reactions, use the abbreviation PEN: Psychogenic, Endocrine, Neurogenic.
Class and exam questions
In a hyperthermic reaction (as in fever), physiological thermoregulation mechanisms remain completely intact; only a temporary imbalance between heat production and heat loss occurs.
In a hyperthermic reaction (as in fever), physiological thermoregulation mechanisms remain completely intact; only a temporary imbalance between heat production and heat loss occurs.
Why can body temperature rise during renal colic or passing stones?
Severe painful irritation of the renal pelvis triggers a reflexogenic hyperthermic reaction. Pain stimulates the sympathoadrenal and thyroid systems, which drastically accelerates metabolism and heat production.
Which drugs most frequently cause an adverse thermogenic effect?
Catecholamine drugs, thyroid hormones, ephedrine, caffeine, and L-DOPA can lead to temperature elevation because they accelerate metabolism and stimulate exothermic processes.
What else to study on this topic
- Topography of the thermoregulation center in the hypothalamus and associated areas of the cerebral cortex and brainstem.
- Biochemical mechanism of the uncoupling of oxidation and phosphorylation processes.
- The role of thyrotropin-releasing hormone and TSH in the pathogenesis of centrogenic heat balance disorders.
- Pathogenesis of sympathoadrenal system activation during psycho-emotional stress and pain syndrome.
- Effect of non-esterified fatty acids, oligomycin, and cyanides on cellular respiration.
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