FRC, lung collapse question

[WanderingGuitarist]

Why does increased FRC cause a greater tendency for the lung to collapse due to elastic recoil?

why does increasing the radius size cause a decreased tendency for the alveoli to collapse?



Thanks!

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[Blind date18]

To ans your second question pressure is inversely proportional to radius ,so smaller the radius greater the pressure inside, as air moves from high pressure to low pressure this tend collapse the alveoli which is counteracted by surfactant . Now coming back to the question larger the radius of alveoli lesser the pressure lower the tendency to collapse ,hope this helps

 

[FindersFee5]

For the first question, interstitial forces in the lung cause increased elastic recoil when the lung volume is larger. Think about stretching out a rubber band: when it's more stretched, the force it's exerting is higher.

 

[Ven0m]

"Increased FRC cause a greater tendency for the lung to collapse due to elastic recoil"
Basically this means the more air inside your lung, the more it wants to recoil back. Like a balloon.

"Why does increasing the radius size cause a decreased tendency for the alveoli to collapse?
An alveolus with a smaller radius has a greater tendency to collapse into itself (deflate) because its smaller. There are fluids lining the inside surfaces of the alveoli, and you know fluids love to come together and hug each other (think of a drop of water. the molecules hug each other together). This is called surface tension. The surface tension is a force that's trying to bring the inside alveolar surfaces together (i.e., collapse). The smaller the radius, the greater the surface tension.

However surfactant lowers this surface tension, so the fluids don't try to "hug" each other as much, thus the tendency of the alveolus to collapse is reduced.

It's kind of confusing how "the smaller the radius the greater the surface tension" works but you can just memorize it like that no need to go deep into physics

 

[WanderingGuitarist]

"Increased FRC cause a greater tendency for the lung to collapse due to elastic recoil"
Basically this means the more air inside your lung, the more it wants to recoil back. Like a balloon.

"Why does increasing the radius size cause a decreased tendency for the alveoli to collapse?
An alveolus with a smaller radius has a greater tendency to collapse into itself (deflate) because its smaller. There are fluids lining the inside surfaces of the alveoli, and you know fluids love to come together and hug each other (think of a drop of water. the molecules hug each other together). This is called surface tension. The surface tension is a force that's trying to bring the inside alveolar surfaces together (i.e., collapse). The smaller the radius, the greater the surface tension.

However surfactant lowers this surface tension, so the fluids don't try to "hug" each other as much, thus the tendency of the alveolus to collapse is reduced.

It's kind of confusing how "the smaller the radius the greater the surface tension" works but you can just memorize it like that no need to go deep into physics

That makes perfect sense!

possible dumb question.

When the lungs expand, what exactly is getting bigger? Is it the parenchyma, alveoli etc.

If the alveoli are getting bigger, so there is a decreased alveolar tendency to collapse during inspiration but everything else wants to collapse?

 

[Ven0m]

"When the lungs expand, what exactly is getting bigger? Is it the parenchyma, alveoli etc."

Technically, inspiration makes the alveoli get bigger because they are filling with air. Their walls (parenchyma) stretch and get thinner when they inflate. Think of it as blowing bubblegum. When you blow a bubble, it's like inflating an alveolus. The walls (parenchyma) stretch and get thinner because more air inside the bubble = higher internal pressure pushing against its walls. Now imagine blowing a triple bubble. The whole thing is the lung and each bubble is an alveolus. When you blow that triple bubble, the lung expands because its alveoli are expanding, and that's what the lung is - a big bundle of alveoli (+airways). But remember that blowing a bubble involves pushing air into the bubble to inflate it. Inflating lungs involves pulling the lungs open so that air rushes in from the outside because of the pressure difference.​

"If the alveoli are getting bigger, so there is a decreased alveolar tendency to collapse during inspiration but everything else wants to collapse?"

Yeah, when alveoli get bigger, the forces promoting their collapse decrease. So, the tendency to collapse is greatest at the end of expiration (but not enough in healthy lungs to collapse them).
What did you mean by "everything else wants to collapse"?​