username459260
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#1
Report Thread starter 7 years ago
#1
I am very confused by the three main pressures within the lung:
* transmural (transpulmonary) pressure
*alveolar pressure
*intrapleural pressure

1) Why does the intrapleural pressure exist? I know it has something to do with the lung recoil and chest wall recoil but why would the chest wall be recoiling? Why is the pressure negative?

2) Does the intrapleural pressure cause the lungs to stay open or collapse?

3) What is the transmural pressure and what is its purpose?

Thanks
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Hype en Ecosse
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#2
Report 7 years ago
#2
(Original post by jsmith6131)
I am very confused by the three main pressures within the lung:
* transmural (transpulmonary) pressure
*alveolar pressure
*intrapleural pressure

1) Why does the intrapleural pressure exist? I know it has something to do with the lung recoil and chest wall recoil but why would the chest wall be recoiling? Why is the pressure negative?
"Negative pressure" just means the pressure inside there is lower than it's surroundings - therefore creating a "suction" effect. This is a pressure inside the pleural cavity - the space between the parietal and visceral pleura. The negative pressure here is important not only in allowing respiration to happen, but also for preventing pleural effusion.

The chest wall and lungs recoil because they're tensile tissues! The chest wall has lots of tense muscles in it that pulls the ribcage back in when you relax the muscles, and the lung is the same - it contains lots of a protein called "elastin", which gives it its "elastic recoil"

2) Does the intrapleural pressure cause the lungs to stay open or collapse?
It depends what the intrapleural pressure is at that time! When your diaphragm contracts, intrapleural pressure decreases and this is what allows the lung to expand. When it relaxes, intrapleural pressure increases and that causes the air to get squeezed back out!
Also, if the pleural cavity is punctured (say, spontaneously or through a stabbing), then the intrapleural pressure can increase and the lung collapses completely - something called a pneumothorax.

3) What is the transmural pressure and what is its purpose?
Thanks
Transmural pressure is sort of abstract, as opposed to actually being present. It's the difference between alveolar pressure and pleural pressure. i.e. it's the pressure difference inside and outside the lung. It's basically the pushing force from inside the lung, which allows them to expand and contract (expand by increasing the pushing force - contract by decreasing the pushing force).
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username459260
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#3
Report Thread starter 7 years ago
#3
(Original post by Hype en Ecosse)
"Negative pressure" just means the pressure inside there is lower than it's surroundings - therefore creating a "suction" effect. This is a pressure inside the pleural cavity - the space between the parietal and visceral pleura. The negative pressure here is important not only in allowing respiration to happen, but also for preventing pleural effusion.

The chest wall and lungs recoil because they're tensile tissues! The chest wall has lots of tense muscles in it that pulls the ribcage back in when you relax the muscles, and the lung is the same - it contains lots of a protein called "elastin", which gives it its "elastic recoil"



It depends what the intrapleural pressure is at that time! When your diaphragm contracts, intrapleural pressure decreases and this is what allows the lung to expand. When it relaxes, intrapleural pressure increases and that causes the air to get squeezed back out!
Also, if the pleural cavity is punctured (say, spontaneously or through a stabbing), then the intrapleural pressure can increase and the lung collapses completely - something called a pneumothorax.



Transmural pressure is sort of abstract, as opposed to actually being present. It's the difference between alveolar pressure and pleural pressure. i.e. it's the pressure difference inside and outside the lung. It's basically the pushing force from inside the lung, which allows them to expand and contract (expand by increasing the pushing force - contract by decreasing the pushing force).
thanks so much for clearing this up
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