MRCP UK EXAMINATIONS

Detailed explanation-1: -People with cystic fibrosis (CF) have increased transport of the salt, sodium across their airway lining. Over‐absorption of sodium results in the dehydration of the liquid that lines the airway surface and (along with defective chloride secretion) is a primary defect in people with CF.

Detailed explanation-2: -In the lung, the CFTR ion channel moves chloride ions from inside the cell to outside the cell. To get out of the cell, the chloride ions move through the center of the tube formed by the CFTR protein. Once the chloride ions are outside the cell, they attract a layer of water.

Detailed explanation-3: -Chloride transport is virtually eliminated because CFTR located on the surface of the cells in the sweat duct is defective. The lack of CFTR function leads to excess chloride in the sweat of people with CF.

Detailed explanation-4: -Cystic fibrosis is associated with a defect in epithelial chloride ion transport which is caused by mutations in a membrane protein called CFTR (cystic fibrosis transmembrane conductance regulator). Heterologous expression of CFTR produces cyclicAMP-sensitive Cl(-)-channel activity.