Wednesday, April 10, 2013

Respiration, Oxygen, and Hemoglobin

By decreasing pressure inside the thoracic cavity, we are able to inspire air.  By contracting the diaphragm, intercostal muscles, and others, we increase the size of the thoracic cavity, which in turn lowers the pressure to the point that it is lower than the outside air, causing a pressure gradient so the air rushes into the lungs.  To exhale, it is the opposite- relax the muscles, decrease the space in the cavity, which increases the pressure inside until higher than outside, so the air rushes out to where the pressure is lower.

This video is a good summary.  The embedding doesn't work, so you'll have to click the link instead.  Just left the embed on there for the picture. :)

Partial Pressure
Total Pressure of air can be broken into the partial pressures of all the gases contained in that air.  For instance, if the atmospheric pressure is at 760 mm Hg, and 20% of that is Oxygen gas, 80% Nitrogen gas, then the partial pressure of O2 would be 20% of 760 = 152 mm Hg.  Partial Pressure of N2would be 80% of 760 = 608 mm Hg.
This illustrates how increasing the pressure, as in the B picture, causes more gas to diffuse into the liquid.  A simple way to think about it is just that the higher the partial pressure of that gas, the less space it has to bounce around in the air, so more of it will end up in the liquid.

Here's a long video on partial pressure and gases getting into solution, I didn't watch the entire thing yet but it looks like a good detailed explanation for those who feel they could use more information.

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