system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does adapting to high altitudes work in the body?

Today is my first day in Bogota, Colombia. Elevation of 2.6km. I don't have altitude sickness like some, but I'm very short on breath after even minor exertion (walking one flight of stairs). 

I know this goes away after 1 - 3 days, but what is actually happening in a person's body to adapt so quickly?
gpt
At high altitudes, the body needs to produce more red blood cells to be able to carry the little oxygen available throughout the body. A similar situation happens with the Badjao tribe, Phillipines, which are regarded as the best freedivers in the world, with spleens 50% larger than normal, and thus can store more blood when the need arises and the ability to stay underwater far longer than average, because they also use the oxygen more efficiently, and they also see clearer underwater than the average human, because they spend so much time in the water hunting fish, IIRC.