What is the primary defect in cystic fibrosis?

Cystic fibrosis is primarily caused by a defect in the CFTR gene, which encodes for the cystic fibrosis transmembrane conductance regulator protein. This protein functions as a chloride channel in epithelial cells, and its malfunction leads to disrupted chloride and sodium transport across cell membranes. This defect results in thick, sticky mucus production in various organs, particularly in the lungs and digestive system.

The inability of the CFTR protein to transport chloride ions properly leads to imbalances in salt and water on epithelial surfaces, causing the mucus to become abnormally thick. In the lungs, this can obstruct airways, promote infection due to the inability to clear pathogens, and cause chronic respiratory issues. In the pancreas, thickened secretions can block pancreatic ducts, impairing the release of digestive enzymes and leading to malabsorption of nutrients.

Understanding the underlying mechanism of CFTR malfunction is key to grasping the pathophysiology of cystic fibrosis and its systemic effects. Other conditions mentioned in the question, such as insufficient insulin production or elevated blood sugars, relate to other metabolic or endocrine disorders and are not the primary issue in cystic fibrosis. Similarly, the production of lung surfactant is generally related to different lung conditions and not directly linked to the