Surfactant Flashcards
What does the Law of Laplace have to do with collapsing alveoli?
Laplace: P = 2 * surface tension / radius.
I.e. As a sphere gets smaller, collapsing pressure gets greater.
Alveoli are very small, so if the surface tension isn’t decreased, they’d be very difficult to open.
Two spheres/ bubbles are connected by a straw with an obstruction that separates them. Bubble A is larger than Bubble B. What happens when the obstruction is removed?
Bubble B (the smaller one) will collapse and empty completely into Bubble A.
What parameter is modified by surfactants?
Surfactants reduce surface tension.
In the case of a water-air interface, this is done via an amphipathic molecule that disrupts H-bonds between water molecules.
What molecules give pulmonary surfactant its amphipathic quality?
Phospholipids.
Some are saturated, for tighter packing.
Some are unsaturated, for greater fluidity.
Why can’t surfactant consist of just phospholipids?
Solution for this?
If you put phospholipids in an aqueous solution, they’ll just form micelles.
Surfactant proteins ensure that the phospholipids stay at the air/liquid interface.
How does surface tension vary during inspiration vs. expiration?
What makes this happen?
Hydrophobic surfactant proteins pull unsaturated phospholipids out of the interface during expiration (area contraction), lowering surface tension.
During inspiration, surface tension increases.
In this way, the collapsing pressure remains constant during inspiration and expiration.
What do the hydrophilic surfactant proteins do?
(which letters are they?)
How do they do it?
SP-A and SP-D have a pro-inflammatory and anti-inflammatory end. These molecules bind bacteria, and when bound, the anti-inflammatory end is hidden, promoting inflammation.
EM description of surfactant storage in Type II alveolar epithelial cells?
Lamellar bodies
How is the relationship between distending pressure and lung volume different during inspiration vs. expiration?
What’s the name for this phenomenon?
Lungs tend to stay distended at lower pressures during expiration (perhaps because there’s less collapsing pressure at higher radii?).
This is called hysteresis, or deflation stability.
How does the relationship between distending pressure and lung volume change if surfactant is deficient?
Less distention for the same amount of pressure.
There is also less deflation stability - they collapse easily. (recall the video on slide 24)
Will residual volume be affected by surfactant deficiency?
Nope. That’s mostly dead space.
What does a developmental (i.e. in premature babies) deficiency of surfactant cause?
Respiratory Distress Syndrome (RDS)
Fetal lungs have fluid in them. This is important. What happens if they don’t have enough?
(not important for this lecture per se, but good to know)
Oligohydramnios -> Potter’s syndrome, which includes lung hypoplasia.
Despite fetal lungs needing fluid in them, they must dry out in the 3rd trimester.
So not only do premature babies not have enough surfactant, but their lungs haven’t dried out all the way either.
What does RDS look like on CXR?
Lungs are underinflated (atelectasis) -> hyperdense, and they don’t extend as low as they should.
