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Causes of bronchial asthma in children
Last reviewed: 23.04.2024
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In the emergence of bronchial asthma, three groups of factors are important:
- genetically determined predisposition of the child's organism to allergic reactions;
- sensitization with exo- and endoallergens;
- factors of the environment that alter the immunobiological reactivity of the organism.
The study of families of children with bronchial asthma suggests that the total contribution of genetic factors to the formation of bronchial asthma is 82%.
A cluster of genes that play a role in the development of bronchial asthma coding for Th 2 -cytokines is located on the long arm of chromosome 5 (5q31.1-5q33). The same region includes the beta-adrenergic receptor gene, which is responsible for altering bronchial reactivity in asthma.
The dominant atopy gene encoding the B chain of the high affinity receptor for IgE is located on the long arm of chromosome 11 in the llql3 region. In the same section, the gene is plotted, the product of which is the phospholipase-A protein, which participates in the synthesis of prostaglandins and leukotrienes, the main mediators of inflammation in bronchial asthma.
Genetic control of a specific IgE response to the allergen is carried out by a group of genes localized in the 6q21.3 site.
Inheritance of bronchial hyperreactivity independent of atopy has been established. The hereditary defect in the synthesis of beta-adrenergic receptors is confirmed by the greater sensitivity of patients with bronchial asthma to adrenomimetics than patients with acute viral obstructive bronchitis.
An innate predisposition forms internal causes of the disease - biological defects that can be genetically determined, and also formed during pregnancy.
Sensitization of the respiratory tract is caused by inhalation allergens - domestic, epidermal, fungal, pollen. Among domestic - it's dust, the fur of domestic animals (dogs, cats), floral plants, down, feather pillows, blankets, etc. Among the pollen allergens - trees, shrubs, cereals.
Medicinal preparations: antibiotics, especially penicillin series, vitamins, serums, acetylsalicylic acid (in children less often).
At the heart of the pathogenesis of bronchial asthma are primarily immunological reactions involving mast cells and basophils, eosonophils, T-lymphocytes.
Under the influence of allergenic stimuli, the T-lymphocyte subpopulation is activated, followed by the release of interleukins (4,6,10,13), inducing hyperproduction of specific IgE, leading to the release of histamine, the chemotactic factor of eosinophils; to stimulation of leukotrienes, prostaglandins (PGE2), platelet activating factor, thromboxane.
Leukotrienes are part of a slow-acting substance that causes a prolonged contraction of the smooth muscles of the bronchi, increases the secretion of mucus, reduces the cilia of the ciliated epithelium. The factor of platelet activation causes platelet aggregation, disturbance of microcirculation, migration of neutrophils, eosinophils.
Great importance in the pathogenesis has a decrease in total and secretory IgA.
A major role in pathogenesis is played by the imbalance of the functional state of the sympathetic and parasympathetic divisions of the higher nervous system.
As the degree of severity of bronchial asthma increases, the patient increases the number of cause-significant factors triggering an attack of bronchial asthma. One of these factors, which play a role in the pathogenesis of bronchial asthma, is SARS. Defeating the bronchial mucosa, it breaks the barrier function, facilitating the penetration of exoallergens, and also leads to the appearance of hyperreactivity of the bronchi.
In such cases it is necessary to speak of infectious dependence as one of the variants of trigger factors. The so-called triggers that cause exacerbations of bronchial asthma, stimulate inflammation in the bronchi and provoke the development of acute bronchospasm are allergens, viral infections, cold air, tobacco smoke, emotional stress, physical stress, meteorological factors.
[Pathomorphology of bronchial asthma
During an attack of bronchial asthma, there is a spasm of smooth muscles of the lungs and large bronchi, edema of the bronchial wall, congestion of the mucus in the airway lumen, cellular infiltration of the sub shell of the mucous membrane and thickening of the basement membrane.