Surfactants, compliance and lung function test Flashcards
What is surface tension?
Alveoli are lined with thin layers of fluid, there is attraction between water molecules that want to be close together and this creates a tension and tendency for alveoli to collapse.
What are surfactants?
Mixture of phospholipids and proteins, they reduce surface tension, increases lung compliance and so make the work of inspiration smaller. They are produced by type II alveolar cells.
Why are surfactants more effective in smaller alveoli?
They are more concentrated there and so molecules are closer together.
Law of LaPlace
P=2T/r
Describe the production of surfactants.
They are produced by type II alveolar cell, it starts at week 25 and finished at week 36. It is stimulated by thyroid hormone and cortisol.
What is IRDS?
Infant respiratory distress syndrome, occurs in premature babies that do not have sufficient amount of surfactants and therefore on breathing they have to overcome tension.
Why is less pressure needed to fill the lungs with saline?
Because there is no water-gas barrier and therefore no surface tension.
Why is needs greater pressure change to reach particular volume of air during inspiration than expiration?
On inspiration we need to overcome surface tension and there is also inertia of the surrounding tissue, it is hardest to start and overcome these.
Why is more air expelled at more positive pressure?
This is due to the resistance of the airways as the air is leaving the lungs(compression of the airways), higher pressure is required to overcome this resistance.
What is lung compliance?
It is the measure of lungs stretchability, but not elasticity. Defined as change in volume for given pressure. High compliance - large change in V for small change in P. It decreases with age.
Is high compliance always good?
No, there is high lung compliance in emphysema, the gradient is steep.
Where is biggest lung compliance and why?
The biggest one is at the base, it is due to gravity as alveoli at the bottom are the most stretched be weight of lungs and therefore have the biggest ability to stretch. This is only true if we are standing, on lying biggest compliance is at the posterior side of the lungs.
Examples of obstructive diseases.
Asthma, chronic bronchitis and emphysema (COPD)
Examples of restrictive lung diseases.
Infant respiratory distress syndrome, lung fibrosis, oedema, pneumothorax
What measurements can be made by spirometry?
Tidal volume, expiratory and inspiratory reserve volume, inspiratory capacity, vital capacity
