Surfactant and Compliance Flashcards
Define surfactant.
A detergent-like fluid produced by Type II alveolar cells.
What is the function of surfactant?
Reduces surface tension on the alveolar surface membrane, reducing the tendency for alveoli to collapse.
Define surface tension.
The attraction between water molecules, where there is an air-water interface.
When is surfactant produced?
~25wks gestation; full term by 40wks.
Stimulated by thyroid hormones and cortisol, which increases towards the end of pregnancy.
Premature babies suffer Infant Respiratory Distress Syndrome (IRDS).
Why does surfactant increase and decrease?
Increases lung compliance.
Increases ease of breathing.
Decreases lung recoil tendency.
Smaller alveoli causes surfactant molecules to come closer together and become more concentrated.
How is pressure controlled by surfactant?
Smaller alveoli will have greater pressure.
Surfactant reduces surface tension, equalising pressure in different sized alveoli.
What is LaPlace’s Law?
Tension within the wall of a vessel with a particular pressure depends on vessel thickness.
Pressure = (2 x surface tension) / radius.
Define compliance.
The change in volume relative to the change in pressure. The stretchability of the lungs.
What affects and determines compliance?
Affected by changes in disease states and age.
Determined by surfactant action.
Describe the relationship between compliance and intra-pleural pressure.
High compliance - a large increase in lung volume, for a small decrease in intra-pleural pressure.
Low compliance - a small increase in lung volume, for a large decrease in intra-pleural pressure.
