Fig. 3

Anatomical distribution of mucus secreting cells in normal airways and pathological alterations in CF. a Mucus is secreted by submucosal glands in the conductive zone and paranasal sinuses. The submucosal glands go on decreasing towards the lowest components of the respiratory zone. In healthy individuals, the cilia of the epithelial cells clear irritants and microorganisms, trapping them in the thin fluidic mucus and clearing by rhythmic ciliary beating upwards known as mucous escalator. In CF, the airway surface liquid layer thins and the mucus comes in contact with cilia resulting in ciliary dyskinesis, causing poor clearance of bacteria which exacerbates inflammation. b Schematic drawing of a single submucosal gland shows serous acini, mucus tubules, and collecting duct. Secretion of water across the epithelium of airway glands is driven predominantly by active secretion of chloride and bicarbonate. The CFTR-dependent water-secreting pathway is defective in CF. Figure adapted from previous publications [54, 55, 57, 59]