chiddler

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bio topic list says:

2. Breathing mechanisms
b. resiliency and surface tension effects

what does this mean?
 

MedPR

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Probably how breathing works (gauge pressure, etc).

Resiliency probably refers to the elasticity of the lungs (used for expansion and recoil). And surface tension is what makes the lungs and alveoli want to collapse; surfactant and IPP counteract that tendency.
 
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chiddler

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what is surface tension in the context of lungs?
 

MedPR

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what is surface tension in the context of lungs?
There's liquid (presumably primarily water) lining the alveoli. Like any other surface tension, the interactions between the liquid molecules pull them closely together and therefore make the alveoli want to collapse.
 

Morsetlis

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Yes, the solvent in the body is water. Water molecules pull together and collapse the alveoli, but that's not the only force. There's also elastic forces due to collagen fibers.

Surfactants (made by your great alveoli cells) dilute and oppose this surface tension. It allows for the expansion of the alveoli, so that you can breathe and inflate them. The smaller the surface area, the closer the surfactant molecules are and the greatest their facilitating effect on opening the alveoli, which opposes the greater wall tension generated by the surface tension (LaPlace's law:
, 4 for 2 surfaces, 2 for 1 surface).
 
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chiddler

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There's liquid (presumably primarily water) lining the alveoli. Like any other surface tension, the interactions between the liquid molecules pull them closely together and therefore make the alveoli want to collapse.
why would they want to collapse?
 

MedPR

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why would they want to collapse?
Surface tension is making them collapse just like it makes water droplets take a spherical shape rather than spreading out into a thin sheet.
 
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chiddler

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So the surfactant is on top of this liquid? How does it prevent collapse?
 

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So the surfactant is on top of this liquid? How does it prevent collapse?
I don't really know, but surfactant is a lipoprotein so I imagine it reduces the interactions of the liquid thereby reducing surface tension.
 
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chiddler

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So some liquid coats the lungs that gives it a high surface tension. There forms a tendency to collapse. But surfactant reduces this tendency somehow.

It still seems weird to use surface tension to describe this because I can see the effect in a liquid but alveoli are spatially separated from each other.
 

MedPR

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So some liquid coats the lungs that gives it a high surface tension. There forms a tendency to collapse. But surfactant reduces this tendency somehow.

It still seems weird to use surface tension to describe this because I can see the effect in a liquid but alveoli are spatially separated from each other.
They're not really separated all that much.



All those white areas are alveoli except for that gigantic one.
 

Morsetlis

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So some liquid coats the lungs that gives it a high surface tension. There forms a tendency to collapse. But surfactant reduces this tendency somehow.

It still seems weird to use surface tension to describe this because I can see the effect in a liquid but alveoli are spatially separated from each other.
Alveoli are roughly spherical. One alveoli collapsing (getting smaller) will push the gas to the other alveoli (getting bigger). Since smaller radius means greater wall tension, it's a positive feedback loop that will eventually turn your 100 alveoli into 10 big alveoli, and then 1 giant alveoli.

Not a good thing.