Mucociliary

Nonciliated cells separate fields of ciliated epithelial cells from each other. Synchronized ciliary movement, with a beat frequency in human proximal airways under normal conditions of 8-15 EIz, propels mucus along the mucociliary escalator at a rate of up to 25 mm/min. Beat frequencies appear to slow to roughly 7 Hz in more distal airways. Cilia move in the same direction and in phase within each field but cilia in adjacent fields move in slightly different directions and are phase shifted. These beat patterns result in metachronal waves that steadily move mucus at higher velocities ( -12-18 mm/min) than would be achievable by summing the motion of individual cilia. 

FIGURE 5.24 Components of ciliary movement, (a) Power and recovery phases of ciliary movement. Arrows indicate the direction of ciliary travel, (b) Net mucociliary transport. Dotted arrows show the direction of cilia while the solid arrows show mucus transport. Note that net gel movement is forward in I and III while no gel movement occurs in II during the cilia recovery phase. Modified from Ful-ford and Blake. ... 

Sulfuric acid (H1SO4) and ammonium bisulfate (NH4HSO4) contribute importantly to ambient acid aerosols, particularly in geographic locations where sulfur-rich coal is used for power plant fuel, such as the eastern United States.Studies on animals and human subjects have shown that H2SO4 and NH4HSO4 alter mucociliary transport in a dose-dependent fashion and... 

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--... 

Reimer, A., von Mecklenberg, C., and Toremalm, N. G. (1978). The mucociliary activity of the upper respiratory tract. III. A functional and morphological study on human and animal mare-tial with special reference to maxillary sinus diseases. Acta Otolaryngol., 1-20. 

Proctor, D. E, Andersen, E, and Lundqvist, G. R. (1977b), Nasal mucociliary funerion in humans, Part 1. In Respiratory Defense Mechanisms pp. 427- 52. Marcel Dekkcr, New York. 

Mucociliary escalator Mechanism that removes extracellularly-derived materials from the conducting airways by entrapping these materials in mucus that is continuously moved toward the epiglottis by synchronized ciliary movement. 

Lungs also secrete nonvolatile compounds. Lipid-soluble compounds may thus be transported with the alveobronchotracheal mucus to the pharynx, where they are swallowed. They may then be excreted or reabsorbed. Particles are also removed by this mucociliary escalator. 

The particle size is the most important factor that contributes to the clearance of particles. For particles deposited in the anterior parts of the nose, wiping and blowing are important mechanisms whereas particles on the other areas of the nose are removed with mucus. The cilia move the mucus toward the glottis where the mucus and the particles are swallowed. In the tracheobronchial area, the mucus covering the tracheobronchial tree is moved upward by the cilia beating under the mucus. This mucociliary escalator transports deposited particles and particle-filled macrophages to the pharynx, where they are also swallowed. Mucociliary clearance is rapid in healthy adults and is complete within one to two days for particles in the lower airways. Infection and inflammation due to irritation or allergic reaction can markedly impair this form of clearance. 

Several groups investigated the use of liposomes for the intra-pulmonary delivery. Farr et al. (1985) showed that the deposition of aerosolized liposomes in the human lung depends on the aerosol particle size. Short-term retention profiles for MLVs and SUVs deposited in the lung were indicative of clearance via the mucociliary transport mechanism. 

Allegra, L., Moavero, N.E. and Rampoldi, C. (1991). Ozone-induced impairment of mucociliary transport and its prevention with M-acetylcysteine. Am. J. Med. 91, 67S-71S. 

While the lung is the major organ exposed to airborne dusts, such agents may also be swallowed following mucociliary transport and removal from the lung. Contaminating particles contained in food and drink also gain direct access into the gut. 

P2-Agonists cause airway smooth muscle relaxation by stimulating adenyl cyclase to increase the formation of cyclic adenosine monophosphate (cAMP). Other non-bronchodilator effects have been observed, such as improvement in mucociliary transport, but their significance is uncertain.11 P2-Agonists are available in inhalation, oral, and parenteral dosage forms the inhalation route is preferred because of fewer adverse effects. 

Airway clearance therapy is usually accompanied by bron-chodilator treatment [albuterol (also known as salbutamol outside the United States) by nebulizer or metered-dose inhaler] to stimulate mucociliary clearance and prevent bronchospasm associated with other inhaled agents. A mucolytic agent may be administered to reduce sputum viscosity and enhance clearance. 

Multiple factors play a role in the development of AOM. Viral infection of the nasopharynx impairs eustachian tube function and causes mucosal inflammation, impairing mucociliary clearance and promoting bacterial proliferation and infection. Children are predisposed to AOM because their eustachian tubes are shorter, more flaccid, and more horizontal than adults, which make them less functional for drainage and protection of the middle ear from bacterial entry. Clinical signs and symptoms of AOM are the result of host immune response and damage to cells caused by inflammatory mediators such as tumor necrosis factor and interleukins that are released from bacteria.4... 

Viscous middle ear effusions caused by allergy or irritant exposure may contribute to impaired mucociliary clearance and AOM in susceptible individuals.4 OME occurs chronically in atopic children, and effusion can persist for months after an episode of AOM. Children with chronic OME usually require tympanostomy tube placement to reduce complications such as hearing and speech impairment and recurrent otitis media. 

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