Although not quite as crucial, there are changes to the digestive and excretory system that will affect you during the hike up the mountain. explain why digestive functions decrease and kidney function increase.

Breathing takes away moisture from the body and at high altitude the air is drier and the oxygen level is lower; because of these factors the kidneys have to acclimatized to these conditions. The kidneys do this by reabsorbing almost all the water that are supposed to be converted to urine in order to conserve enough water for the body. At high altitude, the digestive function of the system decreases, this is because the body redistribute blood due to  insufficient oxygen and reduce the amount of blood that is sent to the digestive system while increasing the amount that is sent to the brain, lungs and the heart. Reduced blood flow to the digestive system can cause nausea.