Co2 Question

[blueface]

We all know that Co2 lowers ph, helps with the release of O2 from the hemoglobins, increases blood acidity and triggers the urge to breathe. My question is, where does the body sense the build up of CO2 that causes the "urge to breathe"?

Does the body sense it in the lungs, blood, tissues or a combination?

I'm guessing that it senses the rising CO2 in the lungs largely because it diffuses into the lungs during the ascent causing blood ph to rise or slow dropping and that is when I feel "air hunger."

My next guess would be in the blood due to the increased acidity. Am I close?

Thanks trux!

 

[Anders]

Since I'm not up to date on human physiology research I'm not sure if anyone have resolved the question of whether the body actually senses CO2 or pH/acidity/H+. At least in fish (which is my area) the question is unresolved, simply because the two are dependent on each other. It's very tricky to change pH without changing CO2 concentration due to the CO2/HCO3/H2CO3 equilibirum in blood or water. The question might be easier to answer in humans, which do not breathe water, what do I know. However, that was all a diversion.

To answer at least part of your question; CO2/ph is sensed, and when breathing strictly controlled, in the blood. Exactly where the sensor cells are located in humans I am uncertain of, but my best guess would be both arterial and venous vessel walls, maybe just one or the other. Other tissues also have methods for maintaining pH homeostasis, but whether they contribute to the urge to breathe I don't know.

 

[blueface]

Thanks Anders! It seems the more I learn the more questions I have.

 

[trux]

Yes, there are both PaCO2 and pH chemoreceptors. If I remember well, the major chemoreceptor groups are in the carotid arteries. However, the process self described earlier in the other thread - the oxygen affinity, etc is not depending on the function of those chemoreceptors.

 

[blueface]

Yes, there are both PaCO2 and pH chemoreceptors. If I remember well, the major chemoreceptor groups are in the carotid arteries. However, the process self described earlier in the other thread - the oxygen affinity, etc is not depending on the function of those chemoreceptors.

Thanks Trux! I am gaining a pretty good understanding thanks to you and the others.

Skip

 

[Bill McIntyre]

I'm not an expert in this, but I always thought C02 was sensed by something in the brain stem.

 

[trux]

Yes, Bill, you are right, there are central chemoreceptor in the "ventrolateral medulla" (a small region of the brain stem), but I was right too - the periferal PaCO2/pH chemorepceptors are in the carotids. There are some differences in their functioning. I found more details for example here:

Chemoreceptors pO2/pH - WikiCNS

 

[blueface]

Very interesting stuff.