Eli5: why are we told to breathe in through your nose and out through your mouth if all the oxygen gets in your blood stream in the lungs either way? Would it not be better to just breathe in and out of your mouth for the most oxygen?

Question

Eli5: why are we told to breathe in through your nose and out through your mouth if all the oxygen gets in your blood stream in the lungs either way? Would it not be better to just breathe in and out of your mouth for the most oxygen?

In: Biology

Answer 1

My physiology prof said that breathing through your mouth is like eating soup through your nose – just because you can, doesn’t mean that you should.
Evolution happened to give us two separate holes with different functionalities. Probably because optimizing managing to eat and breathe at the same time increased successfulness.
In this case the nose performs the function of preparing air: filtering, warming and adding moisture to air that is breathed in, while the mouth (a bigger hole to contain your teeth and tongue alongside salivary glands) performs the function of preparing morsels: ingesting, chopping/grinding and moistening them for swallowing.

edit: The nose, a smaller hole, but a large cavity, contains conchs, small hairs and mucus glands. The first along with the procession from a smaller to a larger space slows the air and creates turbulence, the second filters and the third adds moisture. The slowing is important to enhance the effects of filtering, moistening and warming.