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Inhalation/Exhalation

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Inhalation/Exhalation

Postby biology_06er » Sun Oct 15, 2006 5:13 am

Hi there

I'm studying the respiratory system at the moment and am a little confused about something..can someone please help me out with it...

Ok...so the reason we inhale is due to pressure differences between the pressure in the alveoli and the atmosphere. In order for us to breath in the pressure in the atmosphere must be higher than that in the alveoli and this occurs due to the volume of the lungs/thoracic cavity increasing and hence the pressure decreasing hence air flows from higher region in atmosphere to lower region in alveloi...is this right so far...but my question is we, talk about lowering the diaphragm and elevating the intercostal muscles to do this and due to this reason the pressure decreases BUT when we breath in we are already breathing in Oxygen and whilst doing that our diaphragm is lowering..how can this be?...shldn't it be lowered and THEN we breath in....or have I just got this totally all wrong??...

as I'm writing this I thought if the above was wrong maybe this is right..here goes...when we exhale our diaphragm loweres ence creating the pressure difference and the need to quickly inhale oxygen and then as we inhale the diaphragm elevates hence pressure increase and the need for exhalation is needed...is this right?....please help me....

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Postby sdekivit » Sun Oct 15, 2006 9:34 pm

use the law of Boyle: pV = constant

--> in order to inhale, we assume the situation after exhalation that no air flows.

when we inhale, we increase the lungvolume --> the diaphragm gets flattened and the alveolar pressure decreases. Directly after that (milliseconds) net air flows in because an increase in volume lovers the pressure according to Boyle's law (pV = constant).

The same is valid for exhalation where you assume the situation no air flows after inhalation. The diaphragm relaxes, decreasing the lungvolume. Alveolar pressure therefore rises and air flows out of the lung.
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Postby biology_06er » Mon Oct 16, 2006 5:01 am

Hi there

Thanks for the reply....so the air flowing in and out only occurs MILLI SECONDS after the diaphragm is lowered and elevated??


Thanks
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Postby sdekivit » Mon Oct 16, 2006 7:39 am

biology_06er wrote:Hi there

Thanks for the reply....so the air flowing in and out only occurs MILLI SECONDS after the diaphragm is lowered and elevated??


Thanks
biology_06er


yes, airflow is a direct cause of a pressure change.
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Postby biology_06er » Sat Oct 21, 2006 12:36 pm

but how come it doesn't feel like it takes milliseconds....like when we inhale it feels as though we inhale air as soon as we breath in-i don't see/feel how the diaphragm lowers then the air flow takes place-it looks like it takes place simultaneously!...do you get what i mean?

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