Etiology and risk factors
Disease development is triggered by environmental factors: smoking, infectious agents, air pollution, and various occupational hazards. The condition is closely associated with chronic obstructive pulmonary disease (COPD), which precedes the development of emphysema in the majority of cases.
The most important endogenous factor is genetic predisposition linked to the M gene. Pathological phenotypes (PiZZ, PiSS) result in a congenital deficiency of $\alpha_1$-antitrypsin, the primary protector of lung tissue against enzymatic destruction.
Pathogenesis: how the lungs are destroyed
The morphogenesis of chronic obstructive emphysema is based on two key processes that ultimately merge:
- Protease-antiprotease imbalance. Inflammatory infiltration (histiocytes, polymorphonuclear leukocytes, plasmocytes) and the activation of alveolar macrophages lead to the release of cytokines (IL-8, IL-5). Damaging factors are generated: reactive oxygen species, cathepsins, metalloproteinases, and elastase. Normally, elastase is neutralized by $\alpha_1$-antitrypsin, which is synthesized by hepatocytes and Clara cells. In its deficiency (due to genetics or Clara cell death in chronic bronchitis), lysis of the elastic fibers of the interalveolar septa occurs.
- Valvular mechanism. It develops against the background of pronounced small airway obstruction by mucous plugs or exudate. During inspiration, air enters the alveoli freely, but during expiration, the lumen narrows. Residual air accumulates and overdistends the acinar structures.
Classification and morphological types
Globally, 7 types of emphysema are distinguished: chronic obstructive, chronic focal, perifocal (scarring), vicarious (compensatory), senile, interstitial, and idiopathic.
Depending on the localization of changes within the acinus, 4 morphological variants are distinguished:
- Centriacinar. Only the central parts (respiratory bronchioles, alveolar ducts) are dilated. The periphery of the lobules is preserved. Ventilation failure develops late due to the high compensatory capacity of the tissue.
- Panacinar. The entire acinus is involved. It is characterized by capillary collapse, septal sclerosis, and the development of an air-blood barrier block. The outcome is the rapid development of severe respiratory failure.
- Paraseptal (bullous). Only the distal part of the acinus is altered. It is frequently found in the upper lobes, subpleurally, or around foci of pneumosclerosis. Large air cysts (bullae) up to several centimeters in diameter are formed.
- Irregular. Uneven involvement of the acinus, usually without pronounced clinical manifestations.
Pathological anatomy and complications
Macroscopic appearance: The lungs are markedly enlarged in size, with their edges covering the anterior mediastinum. The tissue is bloated, pale, soft, and does not collapse when the chest is opened. A characteristic crunch is heard on cross-section, and mucopurulent exudate is expressed from the bronchial lumens upon pressure.
Microscopic appearance: The alveoli are dilated and flattened, their septa are thinned. Lysis and fragmentation of the elastic framework are observed. Hypertrophy and hyperelastosis of the closing plates (thickening of the musculo-elastic bundles) form at the alveolar ostia.
Complications: Reduction of alveolar-capillary blood flow and its sclerosis cause microcirculation disorders in the lesser circulation. A fatal cascade is triggered: pulmonary hypertension $\rightarrow$ right ventricular hypertrophy $\rightarrow$ development of cor pulmonale (cor pulmonale). The final stage of the disease is progressive cardiopulmonary failure, requiring mandatory oxygen therapy.
Briefly: answers to topical questions
What are the pathogenetic features of interstitial pulmonary emphysema?
Interstitial pulmonary emphysema is characterized by the penetration of air through alveolar ruptures into the interstitial tissue. A clinical sign is crepitus.
In what conditions does vicarious (compensatory) emphysema develop?
Vicarious (compensatory) pulmonary emphysema develops after the removal of a lung lobe or an entire lung.
What complications and causes of death are characteristic of patients with pulmonary emphysema?
Complications of pulmonary emphysema include progressive cardiopulmonary failure and the development of cor pulmonale due to alveolar-capillary blood flow reduction, pulmonary hypertension, and right ventricular hypertrophy. In chronic focal (perifocal) emphysema, spontaneous pneumothorax may occur. The cause of death can be progressive cardiopulmonary failure.
To easily remember the types of emphysema in relation to the acinus, use the "CPP" rule: Centriacinar (center only), Panacinar (entire acinus — the prefix "pan-" means "all"), Paraseptal (distal part only, forms bullae).
Class and exam questions
What is $\alpha_1$-antitrypsin and why is it needed?
It is a proteinase inhibitor. It protects the elastic fibers of the lung tissue from destruction by enzymes (primarily elastase) released by inflammatory infiltrate cells.
Why do the lungs not collapse upon opening the chest in emphysema?
Due to the valvular obstruction mechanism and the loss of the elastic framework, excess residual air accumulates in the alveoli. The lungs completely lose their elastic recoil.
What is the connection between chronic bronchitis and emphysema?
Chronic bronchitis causes airway obstruction by mucus (triggering the valvular mechanism) and leads to a sharp decrease in the number of Clara cells. This reduces local production of protease inhibitors, paving the way for alveolar destruction.
Which cells normally produce $\alpha_1$-antitrypsin?
The main sources of this protective enzyme in the body are liver hepatocytes and Clara cells located in the epithelium of the terminal bronchioles.
What else to study on this topic
- Genetic phenotypes of $\alpha_1$-antitrypsin deficiency (PiZZ, PiSS, PiMM)
- The role of cytokines (IL-8, IL-5) and reactive oxygen species in the morphogenesis of emphysema
- Mechanisms of air-blood barrier block formation in panacinar emphysema
- Differences between chronic obstructive emphysema and perifocal (scarring) and vicarious emphysema
- The role of desquamation and goblet cell transformation of the bronchial epithelium in pathogenesis
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