Surfactant, Compliance and lung function tests Flashcards
What type of cell makes up alveolar walls?
Thin walled “Type I” cells which permit gas exchange Specialised “Type II” cells which secrete surfactant fluid
What is the function of surfactant?
Reduces surface tension on alveolar surface membrane thus reducing the tendency for alveoli to collapse. Increases lung compliance - distensibility Reduces lung’s tendancy to recoil Makes work of breathing easier
What is surface tension?
The attraction that occurs between water molecules that occurs whenever there is an air-water interface and refers to the attraction between water molecules.
When is surfactant most effective?
In small alveoli than large alveoli because surfactant molecules come closer together and are therefore more concentrated.
What force has to be overcome during inspiration?
Inward force caused by the elasticity of the lungs - they are stretched slightly open even at the end of a relaxed expiration - natural tendency to recoil (contract inwards)
What type of alveoli has the greatest pressure?
The smallest ones
When does surfactant production start? Finish?
25 weeks gestation Complete by 36 weeks
What stimulates surfactant production?
Thyroid hormones and cortisol which increase towards the end of pregnancy
Why is less change in pressure required to inflate lung in utero?
Don’t need to overcome surface tension (no-air water interface)
What is meant by compliance?
Change in volume relative to change in pressure
What is high compliance?
Large increase in lung volume for small decrease in ip (intrapleural) pressure
What is low compliance?
Small increase in lung volume for large decrease in ip (intrapleural) pressure
It requires a greater change in pressure (from FRC) to reach a particular lung volume during inspiration, than to maintain that volume during expiration Why?
Normally effort (work) of inspiration is recovered as elastic recoil during expiration (hence expiration is passive).
What is emphysema?
Toxins in smoke activate elastase causing loss of elastic tissue - means expiration requires effort
What is fibrosis?
Inert fibrous tissue means effort of inspiration increases