Surfactant (PK3)

Question 1

Function of surfactant

Answer 1

Lower surface tension in alveoli

Question 2

Surface tension of pure interstitial fluid

Answer 2

~70mN/m

Question 3

Surface tension of interstitial fluid with surfactant

Answer 3

~2mN/m

Question 4

What is surfactant made of?

Answer 4

• 30-40% DPPC
• 30-45% other phospholipids
• 5-10% protein
• Cholesterols
• Trace amounts of other substances

Question 5

What is surfactant secreted by?

Answer 5

• Alveolar type II epithelial cells

Question 6

2 main regions of surfactant

Answer 6

• Palmitate residues (hydrophobic)
• Phosphate + choline elements (hydrophilic)

Question 7

How does a surfactant molecule prevent surface tension?

Answer 7

• Line the air-liquid interface
• Prevents water molecules reaching interface, where the tangential force of attraction between water molecules would pull them inwards (collapse alveoli)

Question 8

Relationship between surfactant and surface area

Answer 8

Smaller the radius, greater the density of surfactant molecules + greater surface tension lowering effect