Subject: What happens in respiration when a person holds their breath?

I'm trying to understand the process of respiration in relation to aerobic training. I think I understand the "normal" process--oxygen comes in through the lungs, through the alveoli, into the arterial system, on to the cells, back through venous system laden with CO2 to the alveoli, and last of all by osmosis back into the lungs where it is exhaled. Every account in the encyclopedias and online sources tells virtually the same story.

My question concerns the next to the last step as I described it above: my account (like all the ones I've read) make it sound like a one to one relationship between the circulatory system and the respiratory system. Like a miniature conveyor belt in a miniature factory: oxygen comes in on one side of the loop, and CO2 goes out the other side of the loop. You inhale, oxygen is transferred to the blood by osmosis, the heart pumps the blood to the cells, the cells deposit the wasted CO2 by more osmosis on the empty cars which return to the lungs to be exhaled. One breath = one circulatory pump. One to one.

But what happens when you hold your breath?? Where does the CO2 go?

Re: What happens in respiration when a person holds their breath?