Dear Student, At high altitude (height), human tissues suffer from hypoxia. To compensate this lack of oxygen, there is an adaptation to increase the number of RBC's. Increased number of RBC's carry more amount of oxygen and thus provide proper amount of oxygen to all tissues of body. This is long term adaptation. Now, let's talk about short term regulation. In short term regulation, there is hyperventilation (increased rate of breathing) at higher altitudes due to hypoxia such that more oxygen is breathed in. Regards