Alveoli
When they wear large gloves
Easy to stretch the latex.
Small gloves, not so much.
I always remembered Laplace's Law, because of this, I glove surgeons and residents and fellows. I glove myself as well, but my size is average (7.) It's much easier to stretch a size 8 glove (big dudes), much harder a size 6 (for the small females.) Laplace describes why. Those small sacs of the lung are harder to open than the larger ones, or the tubes leading in, they can get clogged and harbor bacteria or tiny, tiny, tiny particles of pollution, and set up a cascade of inflammation. Little balloons are harder to inflate than large ones.
Surface area and volume do not increase equally together.
Important to remember if you want a giant ant menacing the earth in your horror movie. If you care about accuracy, that is.
Application in medicine
In medicine it is often referred to as the Law of Laplace, and it is used in the context of respiratory physiology, in particular alveoli in the lung, where a single alveolus is modeled as being a perfect sphere
In this context, the pressure differential is a force pushing inwards on the surface of the alveolus. The Law of Laplace states that there is an inverse relationship between surface tension and alveolar radius. It follows from this that a small alveolus will experience a greater inward force than a large alveolus, if their surface tensions are equal. In that case, if both alveoli are connected to the same airway, the small alveolus will be more likely to collapse, expelling its contents into the large alveolus.
This explains why the presence of surfactant lining the alveoli is of vital importance. Surfactant reduces the surface tension on all alveoli, but its effect is greater on small alveoli than on large alveoli. Thus, surfactant compensates for the size differences between alveoli, and ensures that smaller alveoli do not collapse.
The Law of Laplace also explains various phenomena encountered in the pathology of vascular or gastrointestinal walls. The "surface tension" in this case represents the muscular tension on the wall of the vessel. For example, if an aneurysm forms in a blood vessel wall, the radius of the vessel has increased. This means that the inward force on the vessel decreases, and therefore the aneurysm will continue to expand until it ruptures. A similar logic applies to the formation of diverticuli in the gut.[7]
Easy to stretch the latex.
Small gloves, not so much.
I always remembered Laplace's Law, because of this, I glove surgeons and residents and fellows. I glove myself as well, but my size is average (7.) It's much easier to stretch a size 8 glove (big dudes), much harder a size 6 (for the small females.) Laplace describes why. Those small sacs of the lung are harder to open than the larger ones, or the tubes leading in, they can get clogged and harbor bacteria or tiny, tiny, tiny particles of pollution, and set up a cascade of inflammation. Little balloons are harder to inflate than large ones.
Surface area and volume do not increase equally together.
Important to remember if you want a giant ant menacing the earth in your horror movie. If you care about accuracy, that is.
Application in medicine
In medicine it is often referred to as the Law of Laplace, and it is used in the context of respiratory physiology, in particular alveoli in the lung, where a single alveolus is modeled as being a perfect sphere
In this context, the pressure differential is a force pushing inwards on the surface of the alveolus. The Law of Laplace states that there is an inverse relationship between surface tension and alveolar radius. It follows from this that a small alveolus will experience a greater inward force than a large alveolus, if their surface tensions are equal. In that case, if both alveoli are connected to the same airway, the small alveolus will be more likely to collapse, expelling its contents into the large alveolus.
This explains why the presence of surfactant lining the alveoli is of vital importance. Surfactant reduces the surface tension on all alveoli, but its effect is greater on small alveoli than on large alveoli. Thus, surfactant compensates for the size differences between alveoli, and ensures that smaller alveoli do not collapse.
The Law of Laplace also explains various phenomena encountered in the pathology of vascular or gastrointestinal walls. The "surface tension" in this case represents the muscular tension on the wall of the vessel. For example, if an aneurysm forms in a blood vessel wall, the radius of the vessel has increased. This means that the inward force on the vessel decreases, and therefore the aneurysm will continue to expand until it ruptures. A similar logic applies to the formation of diverticuli in the gut.[7]
Labels: surgery
Posted by Zhoen on Sunday, January 16, 2011
3 comments:
I was very blessed to have a (gifted) high school physics teacher for a father. So many things boil down to a few fundamental rules of physics and geometry. Things like surface area vs volume. He made the world so *intelligible* to me.
I was dignosed with asthma 7 years ago. and yours is the first explanation of how lungs function on the smallest level that I have found/been given in all this time.
Thank you for this post, Zhoen.
Crow,
There is a difference between obstructive and constrictive lung diseases. Asthma involves reactive airways that clamp down, a spasmodic disease of the bronchi, not the alveoli. The lungs are fine, but you are trying to inflate and deflate them through a coffee stirrer.
COPD is when the alveoli fill with fluid, consolidate, and the surface area for oxygen exchange is reduced. This can happen with long term asthma due to chronic inflammation, but is a different disease mechanism.
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