Cystic fibrosis is a genetic disease that damages the lungs causing difficulty in breathing and chronic pulmonary infections. The disease also affects other organs such as liver, pancreas, and intestines. Half a century ago, the outcome for children with cystic fibrosis was very depressing. These children do not live for more than 10 years, but with medical treatment advancement, cystic fibrosis patients can live for 30 years.
In normal people, an integral membrane protein called CFTR (cystic fibrosis transmembrane conductance regulator) transports Cl- ions out of the cell. A person with cystic fibrosis has a mutated CFTR gene and assembles a defective membrane protein that do not integrate into the cell membrane but instead, destroyed by the cell.
In health lungs, CFTR maintains a negatively charged environment outside the cell by moving out Cl- ions. This negatively charged environment attracts positive ions such as Na+ forming a concentration of Na+ and Cl- in the extracellular space. At the same time, respiratory epithelial cells secrete mucus in the extracellular space that helps trap dust and bacteria. Cilia in the respiratory linings then moves the trapped dust and bacteria out of the respiratory tract. The concentration of Na+ and Cl- helps create a solute-rich mucus that draws water by osmosis from the cell making the mucus thinner and not too viscous. These characteristics make the mucus more effective in protecting the respiratory tissues and help cilia move debris out of the airways.
People with cystic fibrosis lack the CFTR channels and Cl- ions cannot be transported out of the cell in sufficient amount. Consequently, there is a deficiency of Na+ and Cl- ions in the mucus which hinders the movement of water from the cell that should make the mucus thin and watery. The resulting mucus is very thick and sticky making it ineffective in protecting the lungs. Respiratory tracts become blocked by the thick mucus and infection may likely occur due to the cilia not able to move and get rid of bacteria in the airways.
OpenStax Anatomy and Physiology