Particles physiological action

The hazard from inhaled uranium aerosols, or any noxious agent, is determined by the likelihood that the agent will reach the site of its toxic action. Two main factors that influence the degree of hazard from toxic airborne particles are the site of deposition in the respiratory tract of the particles and the fate of the particles within the lungs. The deposition site within the lungs depends mainly on the particle size of the inhaled aerosol, while the subsequent fate of the particle depends mainly on the physical and chemical properties of the inhaled particles and the physiological status of the lungs. 

The physiological effects of exposure to sulfuric acid fumes depend on the particle size of the aerosol. Thus, for a constant sulfuric acid aerosol concentration, the irritant action of the aerosol increases with aerosol particle size. Other factors are humidity, temperature, and previous exposure. Several studies have shown that prolonged exposure to sulfuric acid causes tooth erosion, while overexposure to sulfuric acid aerosols leads to pulmonary edema, chronic pulmonary fibrosis, residual bronchiectasis, and pulmonary emphysema. The thresh-... 

ACh exists in nerve tissue in bound forms in which it is physiologically inert and immune to the action of cholinesterases. This situation can be explained in two ways (1) ACh is chemically free but in the intact tissue it is sequestered within some compartments whose limiting lipoprotein membranes restrict the diffusion of the charged ACh molecules and separate ACh from the cholinesterases (2) ACh is chemically bound to some protein or lipoprotein particles of the nervous tissue. 

It is well known that proliferation or differentiation of nerve or muscle tissue can be enhanced by electrical stimulation, which is in part attributed to the propagation of action potentials upon stimulation. To exploit these physiological events, composites of biodegradable polymers with electroconduc-tive materials have been investigated for effective transmission of electrical signals to the cells cultured on them. PLCL and polyaniline, one of the widely used electrically conductive materials, were mixed to fabricate the nanofiber meshes, illustrating that myotube formation was accelerated when the myoblasts were cultured on polyaniline-containing nanofibers compared to that of PLCL-only nanofibers, even without electrical stimulation (Jun et ah, 2009). Another electroconductive polymer, polypyrrole, was also used as a composite with other synthetic polymers. For example, polypyrrole was incorporated as particles into polylactide scaffolds, and the fibroblasts cultured on them with various intensities of DC current showed controlled proliferation in a current-dependent manner (Shi et al., 2004). 

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