[The morphology of bronchial clearance]

Area of Science:

• Pulmonary Medicine
• Cell Biology
• Respiratory Physiology

Background:

• The airway epithelium secretes mucus, forming a gel layer crucial for trapping inhaled particles.
• Cilia on the airway surface beat to transport this mucus layer, a process vital for lung clearance.
• The periciliary fluid layer (sol phase) is essential for effective ciliary function.

Purpose of the Study:

• To investigate the role of secretions from bronchiolar and bronchial epithelium in human airway clearance.
• To identify the source and function of surfactant structures observed in the periciliary sol phase.
• To elucidate the contribution of surfactant to the overall mechanism of mucociliary clearance.

Main Methods:

• Electron microscopy was used to examine human bronchial and bronchiolar biopsy material.
• Morphological analysis focused on cellular secretions and structures within the mucus layers.

Main Results:

• Clara cells and goblet cells secrete the gel phase of mucus, while peribronchial glands contribute to it.
• Surfactant structures, originating from alveolar pneumocytes II, were identified within the periciliary sol phase.
• This surfactant exhibits surface-active properties, providing an anti-adhesive effect and stabilizing the sol phase's water content.

Conclusions:

• Surfactant produced by pneumocytes II is integral to the bronchiolar and bronchial clearance system.
• Its anti-adhesive and hydrating properties are critical for efficient ciliary mucus transport.
• Morphological findings support the physiological and biochemical evidence of surfactant's key role in lung defense.