Airway Surface Liquid and Respiratory Mucus - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 767

Table 12.3. Ion composition of airway surface liquid in human xenograft model of fetal airways
developed in severe combined immu nodeficiency mice (Sourc e: [ 1560 ]).

Concentration

Ion (mmol/l)

Cl −

65

Na + 64

SO 2 4 5

K +

2

Mg 2 +

2

Ca 2 + 1

12.4.3 Lipids

Lipids represent another important part of mucus molecules (1-2%). Most of the
lipid content is associated with mucin glycoproteins. Phosphatidylethanolamine,
sphingomyelins, and lysophosphatidylcholine raise mucus viscosity, whereas phos-
phatidylglycerol reduces it [ 1557 ].

12.4.4 Surfactant

Constitutive surfactants that are constituted of proteins and phospholipids have
several functions, as they regulate surface tension, control Eustachian tube open-
ing pressure, modify mucus rheology, mitigate oxygen free radical damage, and
decrease inflammation [ 1559 ].
In addition, surfactant components enable sliding of deep gel phase over
superficial sol phase of the liquid interface between flowing air and respiratory
duct wall. Surfactant lowers adhesion at the gel-sol interface so that cilium tips can
better penetrate the gel layer and more effectively propel this layer. Surfactant favors
high ciliary beat frequency, hence mucus speed. Surfactant treatment in infants with
respiratory distress syndrome elevates mucociliary transport rate.

12.4.5 Minerals

Various salts with mono-, di- and trivalent ions account for up to 1% of mucus mass
(Table 12.3 ). Change in ionic content leads to mucus shrinkage or swelling. High
concentration of multivalent cations, such as calcium and magnesium, can facilitate
reversible crosslinking between mucin monomers.