Surfactant

Surfactant:

• Phospholipoprotein complex
  • DPPC – 40%
  • Other phospholipids – 40%
  • Surfactant-associated proteins – 10%
  • Lipids – small amount
• DPCC and other phospholipids have a hydrophilic head, and a hydrophobic tail
  • Align themselves on the interior alveolar surface
  • Intermolecular forces repel each other, reducing surface tension

In an alveolus:

• Surfactant reduces surface tension, increasing compliance
• Surface tension of surfactant changes with alveolar tension
  • At lower volumes, surface tension reduced to near zero
    → Prevents collapse at low volumes
  • At higher volumes, surface tension rises
    → Prevents overdistension
  • Shows hysteresis
• Surface tension draws fluid out of peri-alveolar capillaries
  • Reduced surface tension
    → reduces hydrostatic pressure in capillaries
    → prevents transudate

Mooney 2016

Answer by Mooney