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Asthma - a chronic inflammatory disorder of the airways.

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Asthma Asthma is a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role, in particular, mast cells, eosinophils, T lymphocytes, macrophages, neutrophils and epithelial cells. In susceptible individuals this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness and coughing, particularly at night or in the early morning. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment. The inflammation also causes an increase in existing bronchial hyperresponsiveness to a variety of stimuli. Asthma is characterized by spastic contraction of the smooth muscle in the bronchioles, which causes extremely difficult breathing. Asthma is about 70 percent is caused by allergic hypersensitivity, especially sensitivity to plant pollens. Asthma is a common increasing and relapsing disease that is associated with genetic and environmental factors such as respiratory viruses and allergens. The pathology of asthma is characterised by various changes in the airways including mucus plugging, shedding of epithelial cells, thickening of the basement membrane, engorgement of the vessels, and angiogenesis, inflammatory cell infiltration, and smooth muscle hypertrophy and hyperplasia. The pathogenesis of asthma can be broadly subdivided into inflammatory and remodelling components. The inflammatory features of asthma consist of a dense inflammatory infiltrate in which eosinophils, mast cells, and CD41 helper T lymphocytes predominate. ...read more.


Epithelial damage and loss of its protective barrier function exposes the deeper airway structures to environmental insults, and both inflammatory and structural cells produce several growth factors that lead to angiogenesis, proliferation of smooth muscle in the airway, thickening of basement membranes, and fibrosis. The increase in the mass of smooth muscles in the airway increases bronchial responsiveness by increasing force in response to bronchoconstrictor stimuli and by reduction of the airway's diameter. Smooth muscle in the airways of patients with asthma proliferates excessively in vitro.Important cytokines and enzymes during the remodelling process include transforming growth factor b, epidermal growth factor, and matrix metalloproteinases. Asthma causes significant morbidity and mortality. The changes occurring in the airways consist of a chronic eosinophilic and lymphocytic inflammation, together with epithelial and structural remodeling and proliferation, and altered matrix proteins, which underlie airway wall narrowing and bronchial hyperresponsiveness (BHR). Several inflammatory mediators released from inflammatory cells such as histamine and cysteinyl-leukotrienes induce bronchoconstriction, mucus production, plasma exudation, and BHR. Increased expression of T-helper 2 (Th2)-derived cytokines such as interleukin-4 and 5 (IL-4,5) have been observed in the airway mucosa, and these may cause IgE production and terminal differentiation of eosinophils. Chemoattractant cytokines (chemokines) such as eotaxin may be responsible for the chemoattraction of eosinophils to the airways. The initiating events are unclear but may be genetically determined and may be linked to the development of a Th2-skewed allergen-specific immunological memory. ...read more.


Asthma mortality data offer the longest continuous series, but interpretation is made difficult by the changes in diagnostic classifications (ICD) over time. For Australia, in persons aged 5-34 years, mortality rose from approximately 0.25-0.5 per 100000 person- years prior to 1950 in a linear fashion up to 1.2 per 100000 in 1955, fell briefly, rose to 2 per 100000 in the late 1960's, fell through the 1970's to 1 per 100000, reached a second peak in the 1985 of 1.5 per 100000 and has fallen below 1 per 100000 since then. In age-period-cohort Poisson regressions, there were linear increases in mortality with each 5 year birth cohort since approximately 1930. The only period showing an increase was in the 1960s, with a steady decrease in adjusted mortality into the 1990s, interpreted as due to increased use of inhaled corticosteroids. For reported asthma, the sexes were almost equally affected (51% male). There had been a marked increase in reported long-term asthma at all ages since the 1977-78 Survey, most noticeably in those under 15 years of age, where the prevalence had risen from 4% to 14%. An examination of birthplaces noted the (age-sex adjusted) prevalence of asthma was highest in those born in Australia and New Zealand, next for those from the UK and Ireland, less for those born in Southeast Asia, Africa and Southern Europe, and least for those born in Western Europe. ...read more.

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