Airway surfactant

It appears that a substantial part of the airway surfactant is derived from the alveolar region, but there is also evidence for local production of surfactant. Widdicombe (41) reviewed the possible sources and potential biological role of tracheal surfactants. He concluded that the trachea contains a complex mixture of lipids, including surface-active phospholipids not characteristic of alveolar surfactant. Experiments (60) have shown that nonciliated cells of the bronchioles produce surface-active material and that these cells are involved in ion and water transport. Other studies (43) demonstrated phospholipids in secretory cells of airway submucosal glands, suggeshng local produchon of phospholipids in the... 

In contrast, the mechanical functions of airway surfactant are not well established. One of the functions is particle transport Irom the alveoli to the ciliated airways by a surface tension gradient (78,79), another is particle translocation toward the epithelium in airways. In the present chapter we will focus on the latter mechanical function of the airway surfactant film. 

Bernhard W, Haagsman HP, Tschering T, Poets CF, Postle AD, van Eijk ME, von der Hardt H. Conductive airway surfactant surface-tension function, biochemical composition, and possible alveolar origin. Am J Respir Cell Mol Biol 1997 17 41-50. 

Gehr P, Green FHY, Geiser M, Im Hof V, Lee MM, Schurch S. Airway surfactant, a primary defense barrier mechanical and immunological aspects. J Aerosol Med 1996 9 163-181. 

In eontrast with alveolar surfactant, the source of airway surfactant is less clear (49). Since surfactant material is presumed to leave the tracheal surface by mucociliary transport, the surfactant film has to be replenished by local secretion or from the alveolar region. The two options for the origin of airway surfactant are not mutually exclusive, and it is likely that airway surfactant is derived from both alveolar and local sources. 

Uptake of particles by the epithelium is likely to be enhanced by airway surfactant and could account for the delayed clearance of fine and ultrafine particles from the airways noted in some studies (126,127). Forces from the free energy at interfaces and dividing lines might also contribute substantially to particle-cell interactions. These interactions are considered nonspecific, in contrast with the specific receptor-ligand interactions. Thus, nonspecific interactions could contribute to the uptake of particles by cells that are not professional phagocytes, such as epithelial cells. Epithelial cells of the airways take up particles such as silica and asbestos (128,129). 

The therapy for IRDS includes mechanical ventilation with continuous positive airway pressure. This maintains adequate ventilation and prevents airway collapse between breaths with the formation of atelectasis. Therapy also includes administration of exogenous pulmonary surfactant. Two types of surfactants are used to prevent and treat IRDS in the U.S. These include surfactants prepared from animal sources as well as synthetic surfactants. Exogenous pulmonary surfactants are administered as a suspension (in saline) through the endotracheal tube used for mechanical ventilation. 

Bernhard W, Haslam PL, Floras J (2004) From birds to humans new concepts on airways relative to alveolar surfactant. Am J Respir Cell Mol Biol 30(1 ) 6—11... 

Bronchoconstriction caused by acute exposures to ozone or sulfur dioxide may be expected to change the ventilation distribution, local aerodynamics, and tissue dosage. Edema resulting from exposures to toxic gases may alter the gas-absorptive capacity of the airways, in addition to the aerodynamics. Reaction of irritant gases with surfactant material in the alveoli may alter the absorptive capacity and physical prop-... 

The answer is A. Lung surfactant reduces surface tension of the fluid lining the alveoli to increase pulmonary compliance and facilitate exchange of gases dissolved in that fluid from inspired air into the airway epithelial cells and eventually by diffusion into the blood. Although all the other options represent properties of water or solutions, they have nothing to do with the properties of surfactant. 

Ozone is a powerful lung irritant causing a cough, sore throat, and tiredness. It can also increase a person s sensitivity to allergens. The mechanism may involve oxidation of the double bonds of the fatty acids that make up the surfactants and the membranes of the cells lining the bronchial airways and lungs. 

Niven, R.W. Byron, P.R. Solute absorption from the airways of the isolated rat lung. 2. Effect of surfactants on absorption of fluorescein. Pharm. Res. 1990, 7, 8-13. 

Once a drug aerosol has made its way through the conducting airways to deposit in the deep lung, the major barriers to entering the body are the 0.15 pm layer of type I alveolar cells that are covered by a very thin layer of epithelial lining fluid consisting mainly of surfactant and the relatively permeable endothelium of the alveolar capillaries. Alveolar cells have so called... 

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