The airway epithelial defect in cystic fibrosis is
**Core Concept**
Cystic fibrosis (CF) is a genetic disorder characterized by defective ion transport across epithelial cell membranes, leading to abnormal secretions and impaired mucociliary clearance. The primary defect lies in the CF transmembrane conductance regulator (CFTR) protein, which functions as a chloride channel.
**Why the Correct Answer is Right**
The CFTR protein is responsible for regulating the transport of chloride ions (Cl-) across the apical membrane of airway epithelial cells. In CF, mutations in the CFTR gene result in the production of a dysfunctional protein, leading to impaired chloride secretion and subsequent alterations in the balance of sodium and water across the epithelial layer. This defect causes the production of thick, sticky mucus that clogs the airways and lungs, leading to chronic infections and respiratory complications.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the primary defect in CF is not related to the sodium-potassium pump (Na+/K+-ATPase), which is involved in maintaining the resting membrane potential and regulating sodium and potassium levels in cells.
**Option B:** This option is incorrect because the airway epithelial defect in CF is not primarily related to the release of inflammatory mediators, although chronic inflammation is a secondary consequence of the disease.
**Option C:** This option is incorrect because the CFTR protein is a chloride channel, not a sodium channel, and its dysfunction leads to impaired chloride secretion, not sodium secretion.
**Clinical Pearl / High-Yield Fact**
The CFTR protein is a member of the ATP-binding cassette (ABC) transporter family and is responsible for regulating the transport of chloride ions across epithelial cell membranes. Understanding the molecular basis of CF is crucial for the development of targeted therapies aimed at correcting the underlying defect in CFTR function.
**Correct Answer: D**. The airway epithelial defect in cystic fibrosis is related to impaired chloride secretion due to mutations in the CFTR gene.