Airway lining layer

The surfactant film at the air-mucus interface is probably important for the rheological properties of the extracellular layer by stabilizing the aqueous layer mechanically and by reducing the evaporation of water (54,93). These are well-known functions of surfactant films if spread on top of a water surfaee (94). Fluid balance in the airway lining layer may also be influenced by the recently demonstrated effeet of surfactant in stimulating chloride secretion by airway epithelial cells (95). 

Mercer RR, Russel ML, Crapo JD. Mucous lining layers in human and rat airways (abstr). Am Rev Respir Dis 1992 145 A355. 

Geiser M, Im Hof V, Siegenthaler W, Grunder R, Gehr P. Ultrastructure of the extracellular lining layer in hamster airways is there a two-phase system Mierose Res Technol 1997 36 428-437. 

A realistic boundary condition must account for the solubility of the gas in the mucus layer. Because ambient and most experimental concentrations of pollutant gases are very low, Henry s law (y Hx) can be used to relate the gas- and liquid-phase concentrations of the pollutant gas at equilibrium. Here y is the partial pressure of the pollutant in the gas phase expressed as a mole fraction at a total pressure of 1 atm x is the mole fraction of absorbed gas in the liquid and H is the Henry s law constant. Gases with high solubilities have low H value. When experimental data for solubility in lung fluid are unavailable, the Henry s law constant for the gas in water at 37 C can be used (see Table 7-1). Gas-absorption experiments in airway models lined with water-saturated filter paper gave results for the general sites of uptake of sulfur dioxide... 

Figure 7-2 illustrates a three-compartment structure assumed by McJilton et al. for describing radial diffusion. It consisted of a gas phase in the lumen of the airway, a liquid layer that lined the airway, and a tissue compartment. The rate of movement of the gas into the liquid layer, dm /dt is a function of the solubility of the gas in the liquid, as defined by the Henry s law constant. The rate of movement of the gas molecules across the liquid layer to the tissue compartment, dm /dt is a function of the diffusion co cient of the gas in the mucus and serous... 

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... 

---