Surface tension at the liquid-air interphase in the alveoli makes the air sacs prone to collapsing post expiration.
For sphere-like structures like alveoli, water molecules line the inner walls of the air sacs and stick tightly together through hydrogen bonds.
These intermolecular forces put great restraint on the inner walls of the air sac, tighten the surface all together, and unyielding to stretch for inhalation.
[1] Multiple lung diseases, like ISD or RDS, in newborns and late-onsets cases have been linked to dysfunction of surfactant metabolism.
[2] Released pulmonary surfactant acts as a protective layer to prevent alveolar from collapsing due to surface tension.
[2] SP-B and SP-C are responsible to carry out adsorption of the lipid monolayer at the liquid-air interphase to prevent post expiration atelectasis.
[2] Another important protein that contributes to outcome of surfactant metabolism dysfunction is ABCA3, a transmembrane phospholipid transporter in lamellar body.
Severe deficiency of pulmonary surfactant due to disturbed metabolism of any of these proteins can lead to some form of interstitial lung disease in newborns and adults.
These conditions share similar pathophysiology and overlapping phenotypes because surfactant gene products interactively communicate and control one another.
Surfactant produced by infants with SP-B deficiency is abnormal in composition and does not function normally in lowering surface tension.
Wild-type SP-C proteins are embedded inside the phospholipid bilayer of epithelial type II cell and function to generate and maintain monolayer of surfactant on alveolar surface.
ProSP-C proteins tend to self-accumulate along the secretory pathway, due to high hydrophobic nature, and may activate cellular destruction response.
[4] SFTPC mutation with highest occurrence frequency is substitution of threonine for isoleucine in codon 73, termed I73T, found in more than 25% of patients with SP-C related disorders.
There are more than 150 different mutations throughout ABCA3 gene with various allelic heterogeneity, making it the biggest class of genetic cause of surfactant dysfunction.
Affected surface tension ability results from incomplete formation of lamellar bodies, due to lack of lipid influx by ABCA3.
Overall testings, family history, external factors, and clinical presentations should all be considered to diagnose surfactant metabolism dysfunction.
[citation needed] Neonates with surfactant metabolism dysfunctions, especially those with SP-B disorder, only have lung transplantation as one possible choice of treatment.