Respiratory airway epithelium

The importance of respiratory heat and water losses is not confined to the respiratory structures. Inspiration of cold, hot, or dry air poses the potential threats of thermal injury or desiccation to the airway epithelium" - T8,69 g challenge to whole-body thermoregulation. 

After acute mild insult the nonciliated cells proliferate and the epithelium regenerates to normal. In the airways, nonciliated basal cells are the main proliferating population. In the bronchioles, the Clara cell is the main precursor cell for regeneration. Because of the delicate nature of the respiratory tract epithelium and the close proximity of subepithelial blood vessels, an inflammatory response occurs to all but the mildest form of injury. Many lesions are therefore diagnosed as rhinitis, tracheitis, and bronchiolitis and qualified as acute, subacute, and chronic depending on the stage of the response. 

As shown in Table 18.2, there are many different cell types in the respiratory system with considerable variation in both structure and function from the nasal epithelium to the alveoli. The various cell types of the airway epithelium are shown in Figure 18.2. 

Inhaled air travels along the conductive airways until it reaches the very distal respiratory part formed by the respiratory airways, which are terminated by the sack like compartments of the alveoli. The surface of these air-filled compartments is formed by epithelial cell layers, the alveoli by the alveolar epithelium, respiratory airways by the respiratory epithelium, and conducting airways by the bronchial epithelium (Fig. 1). According to its localization along the airways the epithelial cell layers differs with regard to its cellular composition, epithelial barrier, and transport function. 

NASAL AND PULMONARY EPITHELIUM 7.5.1. The Respiratory Airway Epithelial Barrier... 

Mastronarde JG, Monick MM, Mukaida N et al. Activator protein-1 is the preferred transcription factor for cooperative interaction with nuclear factor-kappaB in respiratory syncytial virus-induced interleukin-8 gene expression in airway epithelium. J Infect Dis 1998 177(5) 1275-81. 

Takizawa, H. et al. (2001) Increased expression of transforming growth factor-betal in small airway epithelium from tobacco smokers and patients with chronic obstructive pulmonary disease (COPD). American Journal of Respiratory and Critical Care Medicine, 163,... 

Inhaled anticholinergics are the most effective class of bronchodilators in COPD patients. Muscarinic receptors are localised to smooth muscle of all airways, but the density decreases down the respiratory tract. They are also localised to airway epithelium and submucosal glands [3]. Four subtypes of muscarinic receptors exist in the lungs and... 

Hansdottir, S., Monick, M. M., Lovan, N. et al. 2010. Vitamin D decreases respiratory syncytial virus induction of NF-kappaB-linked chemokines and cytokines in airway epithelium while maintaining the antiviral state. J Immunol 184 965-74. 

Acute Respiratory Failure Second Edition, edited by WM.Zapol ondF.Lemaire 51. Lung Disease in the Tropics, edited by O.P.Sharma 52. Exercise Pulmonary Physiology and Pathophysiology, edited byB.J.Whipp and K.Wasserman 53. DevelopmentalNeurobiology of Breathing, edited by G.G.Haddad andJ.P.Farber 54. Mediators of Pulmonary Inflammation, edited byM.A.Bray and W.H.Anderson 55. The Airway Epithelium, edited by S. G.Fanner andD.Hay... 

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

Local host defenses of both the upper and lower respiratory tract, along with the anatomy of the airways, are important in preventing infection. Upper respiratory defenses include the mucodliary apparatus of the nasopharynx, nasal hair, normal bacterial flora, IgA antibodies, and complement. Local host defenses of the lower respiratory tract include cough, mucodliary apparatus of the trachea and bronchi, antibodies (IgA, IgM, and IgG), complement, and alveolar macrophages. Mucus lines the cells of the respiratory tract, forming a protective barrier for the cells. This minimizes the ability of organisms to attach to the cells and initiate the infectious process. The squamous epithelial cells of the upper respiratory tract are not ciliated, but those of the columnar epithelium of the lower tract are. The cilia beat in a uniform fashion upward, moving particles up and out of the lower respiratory tract. 

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