Gas Exchange

Great we have gotten air into our lungs, but what happens once it is there?

By now we know that nearly all of the cells in our body need oxygen, but how does the oxygen in our lungs get to our cells. Ultimately the circulatory system will transport the oxygen via the blood, but if the oxygen isn’t in our blood in the first place we have a problem. This is where our alveoli come in!

Our alveoli, the small air-filled sacs at the end of our respiratory bronchioles are crisscrossed with a wide array of blood vessels. Since the alveoli and our blood vessels are only separated by two thin cells the gases inside our alveoli can rapidly move in and out of our blood based on their concentration gradients.

Since oxygen is dropped off at the cells and carbon dioxide is produced there the blood returning to the lungs has a high CO2 concentration and a low O2 concentration. As a result, oxygen rushes into our blood and carbon dioxide rushes out into the alveoli down their respective concentration gradients.

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As the concentration gradients decrease between our blood and alveoli gas transfer slows down and eventually stops when the partial pressures of the gases are equal. The greater the concentration gradient the faster gas shifts and vice versa. This is one reason that getting stuck in a burning building is so dangerous (besides the whole burning to death piece). If the carbon dioxide level in the air is super high we aren’t able to shift CO2 out of our bodies and our blood pH can drop dangerously low.

There is only one issue with this whole process. Our blood can only dissolve so much O2 and CO2 in it. This means that the concentration gradient