Respiratory Physiology Lecture 4 Part 17: Surface tension and the role of surfactant

Question 1

What produces alveolar surfactant?

Answer 1

Produced by Type II alveolar cells

Question 2

Role of alveolar surfactant

Answer 2

• Surfactant lowers the surface tension of the lining fluid so we can breathe without too much effort → improved lung compliance
• Surfactant makes the alveoli stable against collapse → allows communication without collapse

Question 3

Most important component of pulmonary surfactant?

Answer 3

The most important components of the pulmonary surfactant are the phospholipids dipalmitoyl-phosphatidylcholine (DPPC), phosphatidyl-choline, surfactant apoproteins, and calcium ions.

Question 4

Role of phospholipids in surfactant

Answer 4

Due to its hydrophobic and hydrophilic properties, the surfactant gets into the air-water interface and decreases the density of water molecules

• Breaks the strong attractive forces that occur between the molecules of water at the surface

Question 5

What does surfactant reduce?

Answer 5

Surfactant reduces the surface tension of H₂O therefore increasing lung compliance so it is easier to expand the lungs

Question 6

What happens to surfactant with increase surface area?

Answer 6

Thickness of surfactant decreases with increase of surface area → Changes in size with inspiration and expiration; Surfactant on alveoli will be either closer together or farther apart depending on the phase of the respiratory cycle

Question 7

What does surfactant changing with surface area cause?

Answer 7

Thus, it causes T (tension in wall of alveoli) to increase with increasing alveolar diameter. This tends to equalize pressures between alveoli of different sizes, which helps prevent the collapse of small alveoli into larger alveoli (ie. It stabilizes alveoli)

• Therefore there is no pressure gradient between the different sizes of alveoli so air will not go from small to large and hence will not collapse into large alveoli

Question 8

More concentrated surfactant = ?

Answer 8

lower surface tension

Question 9

What do the dynamic properties of surfactant permit?

Answer 9

the dynamic properties of surfactant permit the alveolar surface tension to change with inflation and deflation, as the thickness of the surfactant layer varies inversely with surface area

Question 10

Functions of surfactant

Answer 10

1. Reduces the surface tension of alveolar fluid
2. Stabilizes the alveoli

Question 11

surfactant in premature infants

Answer 11

Lack of surfactant decreases compliance and increases work of breathing

• Have to be administered surfactant to reduce the work of breathing

(Infant respiratory distress, IRDS)