General nosology, characteristic of disease periods. Term-typical path

General nosology, characteristic of disease periods. Term-typical pathological process. Main principles of pathogenesis study.

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1. General nosology

Nosology is the branch of medicine that deals with the definition, classification, naming, and systematic description of diseases.

Core terms

Health: a state of physical, mental, and social well-being, with preserved adaptation and functional reserve.
Disease: a qualitatively new disturbance of normal life activity caused by damaging factors, characterized by impaired regulation, reduced adaptation, structural and functional abnormalities, and compensatory responses.
Etiology: the cause and conditions of disease occurrence.
- Cause: the factor without which the disease cannot arise in a particular situation.
- Conditions: internal or external factors that facilitate, hinder, modify, or predispose to disease but do not independently produce it.
Pathogenesis: the mechanisms and sequence of events through which an etiologic factor causes disease and its manifestations.
Sanogenesis: protective, compensatory, and restorative mechanisms that promote recovery or limit injury.
Symptom: a subjective or objective manifestation of disease.
Syndrome: a stable group of related symptoms caused by a common mechanism.
Diagnosis: identification of a disease based on its manifestations and investigations.
Complication: a new pathological condition that develops during a disease and worsens its course.
Outcome: the final result of disease, such as recovery, chronicity, disability, or death.

Classification of diseases

Diseases may be classified by:

Etiology: infectious, genetic, traumatic, toxic, nutritional, immune-mediated, neoplastic, iatrogenic.
Pathogenesis: inflammatory, autoimmune, ischemic, allergic, metabolic, degenerative.
Organ or system involved: cardiovascular, respiratory, nervous system, etc.
Morphology: for example, pneumonia, hepatitis, nephritis.
Clinical course: acute, subacute, chronic, recurrent, latent.
Epidemiology: sporadic, endemic, epidemic, pandemic.

2. Periods of disease

Although the exact pattern differs among diseases, the usual course includes the following periods.

Period	Main characteristics
Latent period	Time from action of a harmful factor to the first detectable manifestations. In infectious diseases it is called the incubation period.
Prodromal period	Early nonspecific symptoms appear, such as weakness, malaise, low-grade fever, anorexia, or headache.
Period of fully developed disease	Typical clinical signs, syndromes, laboratory abnormalities, and complications are present. Diagnosis is usually most apparent at this stage.
Outcome period	The disease ends in recovery, incomplete recovery, chronic disease, relapse, remission, complication, disability, or death.

Main outcomes

Complete recovery: restoration of structure and function.
Incomplete recovery: residual structural or functional defect persists.
Chronicity: disease continues for a prolonged period.
Remission: manifestations decrease or temporarily disappear.
Relapse: recurrence after apparent recovery or remission.
Recurrence: a new episode of the same disease after recovery.
Death: irreversible cessation of vital functions.

3. Typical pathological process

A typical pathological process is a set of interrelated, stereotyped pathological reactions that develops by common mechanisms in different organs and diseases, despite different causes.

It is not a disease by itself. It can be a component of many diseases.

Characteristics

Polyetiologic: may be triggered by many causes.
Relative stereotypy: follows broadly similar mechanisms and stages regardless of the trigger.
Evolutionary origin: often developed as an adaptive or protective response.
Dual role: may be protective initially but harmful if excessive, prolonged, or poorly regulated.
Occurs in multiple diseases and organs.
Has characteristic structural, biochemical, and functional manifestations.

Examples

Inflammation
Fever
Hypoxia
Edema
Thrombosis
Shock
Stress response
Allergy
Tumor growth
Disturbance of microcirculation
Acid-base imbalance

Example: Inflammation may result from infection, trauma, ischemia, immune injury, or chemical damage. Its mechanisms include vascular changes, increased permeability, leukocyte recruitment, and mediator release. It can remove the injurious stimulus, but excessive inflammation can cause tissue damage.

Distinction from related concepts

Pathological reaction: a short, inadequate, or exaggerated response to a stimulus, for example an allergic reaction.
Pathological process: a sequence of pathological reactions with a common mechanism, for example inflammation.
Pathological condition: a persistent structural or functional abnormality, often the result of a previous disease or injury, for example a scar, valve deformity, or loss of a limb.
Disease: a broader, integrated disorder of the whole organism, with a specific cause, pathogenesis, manifestations, course, and outcome.

4. Main principles for studying pathogenesis

1. Principle of causality

Every pathological event has a cause. Pathogenesis must establish the causal sequence from the etiologic factor to molecular, cellular, tissue, organ, and systemic manifestations.

2. Unity of etiology and pathogenesis

The cause initiates disease, but disease development depends on the body response and subsequent pathogenic mechanisms. Removing the cause may not always stop disease if self-sustaining mechanisms have developed.

Example: An infection may initiate sepsis, but cytokine excess, endothelial dysfunction, coagulation abnormalities, and circulatory failure can continue even after microbial control.

3. The leading link

The leading link is the central mechanism that determines the development or progression of a pathological process. Identifying it is important because its correction can interrupt multiple downstream changes.

Example: In diabetes mellitus, insulin deficiency or insulin resistance is a leading link in hyperglycemia and its metabolic consequences.

4. Vicious circles

A vicious circle occurs when one pathological change aggravates another, which then reinforces the original disturbance.

Example: Blood loss causes hypotension, reduced tissue perfusion, hypoxia, acidosis, impaired cardiac function, and further hypotension.

5. Structural and functional unity

Structural damage and functional disturbance are interdependent. Functional changes may precede visible structural injury, while structural injury can later produce persistent dysfunction.

6. Local and systemic unity

A local process can produce systemic effects through neural, endocrine, immune, humoral, and circulatory mechanisms. Conversely, systemic disorders can manifest locally.

Example: Local inflammation can cause fever, leukocytosis, increased acute-phase proteins, and systemic inflammatory response.

7. Specific and nonspecific mechanisms

Specific mechanisms depend on the particular cause or disease, such as autoantibodies in autoimmune disease.
Nonspecific mechanisms occur in many diseases, such as stress, fever, hypoxia, inflammation, oxidative stress, and microcirculatory disorders.

8. Role of reactivity and resistance

The same harmful factor can produce different outcomes depending on age, genotype, immune status, endocrine state, nutrition, prior disease, and environmental exposure.

9. Protective and damaging mechanisms coexist

Compensation and adaptation can limit harm, but may become pathogenic when excessive or prolonged.

Example: Tachycardia initially maintains cardiac output, but sustained tachycardia increases myocardial oxygen demand and can worsen heart failure.

10. Dynamic and stage-dependent nature of disease

Pathogenesis changes over time. A mechanism important at disease onset may be less relevant later, while complications may become the main threat. Therefore, treatment should be targeted to the stage and dominant mechanism of disease.

Short summary

Nosology studies disease concepts and classification.
A disease usually passes through latent/incubation, prodromal, fully developed, and outcome periods.
A typical pathological process is a stereotyped mechanism, such as inflammation or hypoxia, shared by many diseases.
Studying pathogenesis requires identifying cause-effect relationships, the leading link, vicious circles, compensatory mechanisms, and local-to-systemic interactions.

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