enter these ultimate areas and those that cannot. As a rough guide, about 90% of 5-micron particles will pass into it, 50% of 7-micron particles will penetrate it and only about 5% of 9-micron particles will do so. The Pulmonary System The pulmonary system can be conveniently divided into three parts: nasal, middle lung and alveolar sacs. Each area is quite complex. Over a thousand biotechnical articles have been written to explain how they operate. The nasal vestibules contain turbinates and other mucosal blanket structures that capture nearly all liquid and solid particles in the 18–200 micron range. Examples are water mists, salt water fogs, smoke, saw dust and plant pollen. Smaller particles pass through the trachea and enter the middle lung, where they are typically warmed and humidified, often growing somewhat in size. They pass through a maze of bronchi and bronchioles, which are bent and bifurcated about 22 times before finally ending in the alveolar sacs. The bronchial walls of smooth muscle are lined with films of ciliated mucosa—thin layers of viscous liquid, into which tiny hairs are embedded. These cilia flex constantly upward, elevating impacted particles into the trachea at about 0.40" (10mm) per minute, from which they can be either swallowed or expectorated. The mucocilial protective films extend down to the last few bifurcations, where the bronchiole’s inside diameter shrinks to about 0.020" (0.5mm). There is no longer any room for the film. Particles, typically below about 7-microns in diameter, that penetrate this far will deposit primarily on the bare walls of the alveolar sacs, sometimes with life threatening consequences. The pulmonary system is one of the body’s largest organs, with an area of about 70 square meters. It contains about 150,000 respiratory bronchioles and they ultimately divide into some 26 million ducts, leading to about 60 million alveolar sacs, and finally to around 400 million alveolae. The alveolae, with their semi-permeable transpirational surfaces, festoon the wall of each sac. The transpirational areas must be kept essentially intact so that they can efficiently absorb oxygen and eliminate carbon dioxide in the breathing process. Solid particles, such as silica and coal dust, rarely interfere. They act by inducing inflammation, bronchial swelling and cancers. The inhalation of the herbicide Agent Orange has caused kidney failure in Vietnam War veterans. During the collapse of the World Trade Center buildings in New York City, first responders inhaled silaceous concrete dusts, carbon filaments and other fine particles, often with resulting chronic health disorders. On rare occasions, mucosal fluid may extend into the sacs or salinated water may flood the sacs, causing heart failure or other problems. Lastly, film-forming liquids, such as silicones, may block some of the transpiration sites, causing responses ranging from heavy breathing to asphyxiation. Liquid particles that reach the alveolar sites by impaction (inertial deposition), diffusion, sedimentation or other mechanisms are cleared in days, months or even years by such events as evaporations, penetration, chemical reactions and so forth. The most challenging types are Examples of bronchial angulations and bifurcations, designed to capture particles by impaction. A cluster of alveolar sacs. Each sac carries about six to eight alveolar transpirational surfaces. March 2016 Spray 23
Spray March 2016
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