Kidneys can regulate the acidity or alkalinity of the plasma varying the excretion of hydrogen and bicarbonate ions. In alkalosis (abnormally high level of the plasma pH) the kidneys excrete more bicarbonate and the equilibrium of formation of bicarbonate from water and carbon dioxide shifts towards formation of more hydrogen ions and bicarbonate and then the plasma pH is lowered. When the body undergoes acidosis (abnormal low level of the plasma pH) the kidneys excrete more hydrogen ions and retain more bicarbonate thus the equilibrium of formation of bicarbonate from water and carbon dioxide shifts towards more hydrogen consumption and the plasma pH is increased.