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Why does cystic fibrosis cause unusually thick and sticky mucus?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — respiratory disease The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

Cystic fibrosis (CF) causes the production of unusually thick and sticky mucus due to a dysfunction in the cystic fibrosis transmembrane conductance regulator (CFTR) protein.1

In healthy individuals, the CFTR protein regulates the transport of chloride ions across cell membranes, which is essential for maintaining the proper fluidity of mucous secretions. In most cases of CF, a genetic mutation results in a defective CFTR protein. This defect causes chloride and sodium ions to accumulate inside cells, which draws fluid out of the surrounding mucus and into the cells. This process leads to the dehydration of the mucus that normally coats the surfaces of the respiratory and digestive tracts.1

Additionally, the disease is characterized by the secretion of substances containing higher-than-normal concentrations of protein and calcium, which further increases the viscosity of these secretions. This thick, sticky mucus accumulates in the lungs, plugging the bronchi and creating an environment that promotes chronic respiratory infections.21