In multiple pulmonary diseases including cystic fibrosis and chronic bronchitis the process of MCC is defective. This leads to lack of clearance of viruses, bacteria and pollutants resulting in lung infections which can irreversibly damage the lung.
The underlying reason for the failure of MCC in these diseases is an imbalance in the amount of mucus, which is stored in a desiccated form in mucus producing goblet cells, and the fluid available to hydrate the mucus.
The result is a mucus gel which is thick and sticky and cannot be moved by the ciliated cells enabling bacteria and viruses to cause infections.
Furthermore, in excess this mucus can also cause blockages in the airways making it difficult to breath effectively. This fluid imbalance can result from either a reduction in the amount of fluid (airway surface liquid) available in the lungs and/or an increase in the number of mucus producing cells (see figure 2):