C The respiratory Airways
The respiratory tract airways room lined by a pseudostratified columnar epithelium through a selection of unique cell species including ciliated and also goblet cells that play critical roles in mucociliary clearance and host defense. Overlying the epithelium is a thin layer of airway surface ar liquid (ASL) written of a watery sol that washes end the protruding cilia overlaid by a mucus gelatin that trap debris in the inhaled air. In common mucociliary clearance, beating that the cilia in the watery sol propels mucus up the airways, remove debris indigenous the lungs. Defective epithelial ion transport in CF prevents normal mucociliary clearance, bring about the accumulation of thick sticky mucus and airway obstruction. Distinct from various other organs influenced by CF, over there is also a localized fail of the hold defense system in the respiratory tract airways through the an outcome that CF airway disease is defined by persistent bacterial infections (Welsh et al.
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Like sweat duct epithelia, airway epithelia possess both CFTR and also ENaC networks in their apical membrane. They are additionally endowed with a similar repertoire the basolateral membrane transporters come those uncovered in secretory epithelia (e.g., the intestine). Together a result, airway epithelia are qualified of both absorbing or secreting fluids and electrolytes depending upon the prevailing electrochemical gradients and also neurohormonal signals (Welsh et al., 2001). CF airway epithelia are defined by 2 defects in transepithelial ion move (Wine, 1999). First, the Cl− permeability the the apical membrane is substantially reduced and also unresponsive to cAMP agonists. Second, the Na+ permeability the the apical membrane is amplified dramatically. Two different hypotheses have been suggest to explain the pathogenesis of CF lung disease. The high salt theory is based on the role of CFTR together a regulated Cl− channel (Smith et al., 1996), whereas the low‐volume theory emphasizes the duty of CFTR together a regulator the ENaC (Matsui et al., 1998; Guggino and also Stanton, 2006). In the high salt hypothesis, the NaCl concentration of ASL continues to be elevated together a an effect of the fail of CFTR‐driven salt and water reabsorption. The high salt content of ASL inactivates antimicrobial substances bring about a localized failure of the hold defense system in the respiratory airways (Smith et al., 1996). Through contrast, in the low‐volume hypothesis, CFTR dysfunction disinhibits ENaC resulting in the unrestrained absorption of fluids and also electrolytes. This increased absorption depletes ASL volume and also dehydrates mucus resulting in the failure of mucociliary clearance (Matsui et al., 1998). Strikingly, the high salt and also low‐volume hypotheses indicate opposing treatment regimes for CF lung disease.
The proximal airways likewise contain submucosal glands with serous, mucous, and also cuboidal epithelial cells. Engelhardt et al. (1992) demonstrated that serous cells of the submucosal glands space the predominant site the CFTR expression in the respiratory tract airways. CFTR‐driven fluid and also electrolyte secretion by these cells flushes mucins, glycoconjugates, and antimicrobial substances exit from the mucus and also serous cells out of the submucosal glands and into the lumen that the airway where they play crucial roles in mucociliary clearance and host defense (Welsh et al., 2001). Break down of CFTR in CF reasons the blockage of submucosal gland ducts, avoiding the shipment of substances come the airway lumen. CFTR dysfunction might also reduce the volume and/or transform the composition of secreted liquid with the result that the viscoelastic properties of mucus and also the ingredient of ASL space perturbed (Welsh et al.
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, 2001). Come summarize, CFTR theatre a number of crucial roles in the respiratory airways, that dysfunction causes the facility problem the CF lung disease.