Respiratory Physiology 2.3- Surfactant and Compliance Flashcards
What are the alveolar wall cell types?
Type I cells- thin walled and permit gas exchange
Type II cells- secrete surfactant fluid
Give characteristics of surfactant?
reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
unhelpful if the alveoli collapse as requires extra effort to inflate the alveoli from a collapsed position
How does surface tension occur?
occurs where ever there is an air water interface and refers to the attraction between water molecules
Where do we find an air-water interface and why?
on the surface of the alveoli because the middle of the alveoli is filled with air.
Air needs to be fully saturated before it can diffuse from the alveoli into the blood and it gets saturated on the surface of the alveoli
What does surfactant do?
sits between water molecules around the alveoli and effectively reduces the attraction between those water molecules
reduces surface tension (T)
Pressure is equalized in the large and small alveoli
Give characteristics of surfactant?
Detergent like fluid produced by Type II Alveolar cells
Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
Increases lung compliance (distensibilty)
Reduces lung’s tendency to recoil
Makes work of breathing easier
Is more effective in small alveoli than large alveoli because surfactant molecules come closer together and are therefore more concentrated.
What is the Law of LaPlace?
Pressure (P)= 2T/r
T=surface tension
r=radius
What is likely to happen to a smaller alveoli?
pressure is greater in the small alveolus
alveoli would tend to collapse and force its air into the larger alveoli
and have a large alveoli instead of a medium size one and a small one
Why is air from medium sized alveoli and small alveoli going into a large one not good?
less surface area availible for gas exchange
When does surfactant production start?
At 25 weeks gestation when there is an increase in thyroid hormone and cortisol we get towards the end of pregnancy
What is infant respiratory distress syndrome?
babies find it difficult to breathe as they don’t have adequate amounts of surfactant
What can be given to babies with infant respiratory distress syndrome?
aerosols of synthetic surfactant
How much pressure does it take to fill lungs with saline and with air?
much less pressure to fill lungs with saline
What are babies inhaling when they are in utero?
breathing in uterine fluid which is effectively saline.
What do you get from the placenta?
oxygen from mother and getting rid of carbon dioxide
