Surfactant

SURFACTANT

• Soap-like substance secreted by type-II pneumocytes of alveolar epithelium
• Major role in maintaining the lung compliance.

Embryological facts on surfactant:

• Surfactant synthesis occurs in 24 – 28th  week of gestation
• Amniotic fluid appearance in 28 – 32nd week.
• Pre-term conditions – Deduction in 28th week.
• Mature levels of surfactant after 35th week

Composition:

• Surface-active lipoprotein complex (phospho-lipo-protein)
• Main surface tension lowering phospholipid in surfactant
• Dipalmitoyl-phosphatidylcholine (DPPC) (dipalmitoyl-lecithin)

Other substances present include:

• Phosphatidylglycerol
• Neutral lipids
• 4 Surfactant proteins (SP – (A to D)
• Carbohydrates
• Other phospholipids.

Mechanism of action:

• Breaking water molecule inside alveoli:
• Water molecule lining alveoli exert elastic contractile force
• Resulting in alveolar collapse
• Surfactant breaks this surface tensional force of water molecules.

Functions:

• Acts on alveoli
• Reduces surface tension of fluid-lined alveoli
• Prevents lung and alveolar collapse
• Increases lung compliance
• Prevents pulmonary edema

Special physiological effects:

• Reduction in alveolar surface tension.
• Reduces collapsing tendency of alveoli & lungs.

Alveolar stabilization:

• Is a property of alveoli to reduce natural tendency of smaller alveoli to collapse into larger ones.
• Also, reduces tendency of alveolar interstitial fluid transuding out to alveolar space
• Reduces alveolar elastic recoil.

Effects of surfactant deficiency:

• Decreased compliance
• Increased elastic recoil
• Hyaline membrane formation
• Atelectasis
• Interstitial edema

Conditions associated with surfactant:

1. Acute Infant Respiratory Distress Syndrome (IRDS)

• Also referred “Hyaline membrane Disease” (HMD)
• In premature infants
• Glucocorticoids accelerate surfactant production in premature lungs

Cause:

• Due to Immature functional surfactant system
• Insufficient production of surfactant dipalmitoyl lecithin

Treatment:

• Corticosteroid administration to pregnant women.
• Transplacental transport to fetus promote,
• Accelerated fetal lung maturation.
• Production of surfactant.

2. Cigarette smoking:

• Decreased surfactant