protection of lungs with mucin
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38 Terms
How many particles do the lungs encounter daily?
About 2 × 10¹¹ particles.
What is the primary defense mechanism of the lungs?
The mucociliary escalator — mucus traps particles and cilia move them upward for clearance.
how fast does mucus move via mucociliary transport?
About 60 μm/s.
What happens if there’s too much mucus?
Cilia become immobilized, mucus clearance is reduced, and infection risk increases.
What happens when mucus overproduction causes tearing from the epithelial layer?
Tissue damage, airway obstruction, and increased infection risk (e.g., Pseudomonas aeruginosa in cystic fibrosis).
Where are mucins synthesized?
In goblet cells and stored in secretory granules.
What triggers mucin secretion?
An extracellular signal (often Ca²⁺-dependent).
What happens during mucin synthesis?
Proteins dimerize in the ER, undergo O-glycosylation in the Golgi, then polymerize and condense before packaging for secretion.
How much can mucins expand after secretion?
Up to 100–1000× their stored volume.
What allows mucin expansion during secretion?
Calcium–sodium ion exchange and water influx.
What is the role of bicarbonate in mucin expansion?
It removes Ca²⁺ from mucins, promoting unfolding and hydration.
What physical properties does secreted mucus have?
It forms a viscoelastic gel ideal for trapping particles and aiding transport.
Which mucins are found in the airways?
MUC5B and MUC5AC.
Where are MUC5B and MUC5AC produced?
Both in upper airways; MUC5B in submucosal glands and MUC5AC in surface goblet cells.
Are there submucosal glands in the lower airways?
No, mucus there is secreted by epithelial goblet cells.
When is MUC5AC upregulated?
During inflammation and type 2 allergic responses.
What is the essential role of MUC5B?
Mucociliary clearance and bacterial clearance — necessary for survival.
What happens if MUC5B is knocked out?
Clearance fails, bacteria accumulate, and mice die even with antibiotics.
How do MUC5AC and MUC5B differ structurally?
MUC5AC: forms crosslinked, condensed networks
MUC5B: forms open, bundled networks
How do MUC5AC and MUC5B differ functionally?
MUC5B enables clearance
MUC5AC strengthens protection and mucus orientation
What causes cystic fibrosis (CF)?
A defect in the CFTR Cl⁻ channel, disrupting ion and water transport.
How does CF affect mucus properties?
Mucus becomes dehydrated, sticky, and poorly expanded, impairing movement.
What happens to cilia in CF airways?
Cilia are compressed and immobilized by thick mucus, even though their length is unchanged.
What is the result of mucus accumulation?
Impaired clearance, infection, and tissue damage.
Which pathogen commonly infects CF lungs?
Pseudomonas aeruginosa.
What are the two layers in airway mucus?
Periciliary layer (PCL): watery layer allowing cilia movement
Mucus gel layer: traps particles above PCL
What does the periciliary layer do?
Maintains osmotic pressure and keeps mucus from compressing cilia.
What happens when mucus becomes too concentrated (>1–2% solids)?
Pore size decreases, the layer thickens, and cilia become trapped.
What is the periciliary brush theory?
transmembrane mucins form a negatively charged polymer brush around cilia that repels the mucus gel.
Why is osmotic pressure important for mucus stability?
Higher osmotic pressure in the PCL keeps the mucus layer lifted and prevents collapse.
How is osmotic pressure related to pore size?
π ∝ 1/r² — smaller pore size increases pressure.
What does the polyelectrolyte brush model describe?
The balance between PCL and mucus gel layers, determined by mucin charge, pore size, and ion concentration.
What role does calcium play in mucin storage?
It crosslinks mucins in granules, keeping them compact.
what happens when calcium is removed from mucins?
The network expands and unfolds, forming a hydrated gel.
What regulates mucin crosslinking and expansion?
Calcium binding, bicarbonate buffering, and ionic strength.
What are potential strategies to improve mucociliary clearance?
Breaking mucin–mucin covalent or ionic bonds
Disrupting mucin–protein interactions
Modulating secretion machinery
Restoring ion transport (CFTR therapies)
How does proper mucus clearance depend on ionic balance?
correct Cl⁻, Na⁺, and HCO₃⁻ levels ensure proper hydration, expansion, and mucus flow.
What defines healthy airway mucus?
Balanced viscosity, hydration, and coordinated ciliary beating.
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