Airways defense mechanisms

Airway defense mechanisms Group of physical, physiological, and immu-... 

Disruption of these defense mechanisms can lead to bacterial colonization or viral infection. Mucus temperature is important in controlling respiratory infections because decreasing below central body core temperature not only impairs ciliary movement,hut also enhances viral replication,- greatly increasing the likelihood of respiratory infection. Drying of airway mucus also increases the possibility of respiratory infection by reducing mucus thickness and impairing mucociliary clearance, i- i--... 

Knowles MR, Boucher RC (2002) Mucus clearance as a primary innate defense mechanism for mammalian airways. J Clin Invest 109 571—577... 

In experimental animals the respiratory system is a primary target of acrolein exposure after inhalation, and there is an inverse relationship between the exposure concentration and the time it takes for death to occur." Inhalation LCso values of 327ppm for 10 minutes and 130ppm for 30 minutes have been reported in rats." Of 57 male rats, 32 died after exposure to 4 ppm for 6 hours/day for up to 62 days. Desquamation of the respiratory epithelium followed by airway occlusion and asphyxiation is the primary mechanism for acrolein-induced mortality in animals." Sublethal acrolein exposure in mice at 3 and 6 ppm suppressed pulmonary antibacterial defense mechanisms. A combination of epithelial cell injury and inhibition of macrophage function may be responsible for acrolein-induced suppression of pulmonary host defense. ... 

However, the lungs are equipped with defense mechanisms especially with regard to the intake of foreign substances from the air. Thus, the upper airways of the respiratory system are lined with ciliated cells, and mucus is secreted, which also lines the airways. Solid particles are therefore trapped by the mucus and cilia and are transported out of the respiratory system. Other substances may be removed after dissolving in the mucus and then being transported out by the ciliary escalator. 

There are two important defense mechanisms against inhaled particles. The first of these involves the mucociliary escalator and consists of the trapping of particles in mucus followed by the upward movement of the mucus brought about by the upward beating of cilia on the airway epithelial airway cells. The material is then either swallowed or expectorated. The second mechanism is macrophage mediated. Macrophages engulf particles and either deposit them on the mucociliary escalator or enter the lymphatic system. 

The adult human lung is exposed to more than 10,000 litres of air each day. Thus with each intake of air, the lung receives a high burden of dusts, fumes, pollens, microbes and other contaminants. Efficient defense mechanisms have evolved to minimize the burden of foreign particles entering the airways, and clearing those that succeed in being deposited. 

Defense Mechanisms of the Airways against Aspergillus fumigatus ... 

We believe that treatment with antibiotics for chronic airway infection is naturally limited, because chronic airway infection is different from acute airway infection in terms of the disease process. First, chronic airway infection exists for certain reasons, i.e., a defect of the defense mechanism of the airway. Second, chronic airway infection is accompanied by an inflammatory process, which results in the vicious circle proposed by Cole [38]. Presently, we think that EM blocks the vicious circle in chronic airway infection as it inhibits the inflammatory process (Fig. 5). 

C-fibres play an important role in airway defensive reflexes. They respond to both mechanical (though with a higher threshold than A5-fibres) and chemical stimuli, including sulphur dioxide, capsaicin and bradykiiun (Lee et al. 2001). In certain species they evoke the peripheral release of neuropeptides such as substance P, neu-rokiiun A and CGRP via an axon reflex which leads to bronchoconstriction and... 

Particles (such as those present in mists, and in fumes, smokes, and dusts) present a more complex distribution pattern because the particle size affects its deposition at various levels of the airway. Such factors as sedimentation and impact rates also control particle deposition. Therefore, heavier particles may settle in the nasopharynx or upper airways, whereas lighter or smaller particles may reach more-peripheral airways. Once they have impacted, particles are susceptible to a variety of respiratory defense mechanisms. These mechanisms determine the efficiency with which particle removal progresses, thereby determining the particle s ultimate degree of adverse effects. 

The major means by which beryllium enters the body is by the respiratory tract. Since particles greater than 5 )im in diameter will usually be cleared by the mucociliary defense mechanism and either expectorated or swallowed, retention of beryllium is thought to occur only if particles less than 5 xm are inhaled. Particles of less that O.S p.m tend to remain in suspension and are not retained by the lungs. Thus, only particles between 5 and O.S p.m should be retained in the lungs. Both soluble and insoluble forms of beryllium will precipitate when they impact tissue in the distal lower airways. Beryllium appears to be cleared by the lungs in two phases. The first phase is fast with a half-life of several hours to 2 months. The second phase is slow with a half-life from one-half to several years [8-10]. It is probable that once inhalation of beryllium occurs, it is never completely eliminated. 

The structural configuration of the nasal and oral passageways markedly restrict the access of large particles to the lower respiratory tract. Under normal circumstances, the filtration system of the upper airway and the mucociliary clearance system of the larger airways protect the lower respiratory infection from bacteria that may be present in the patient s environment or that reside in the upper respiratory tract. Nosocomial pneumonia and tracheitis may occur when the mucociliary and cellular defense mechanisms of the lower respiratory tract are evaded. 

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