The renal system maintains normal acid-base balance by reabsorbing bicarbonate and excreting hydrogen ions. It reabsorbs more bicarbonate than the respiratory and chemical buffers. Bicarbonate is reabsorbed at the proximal collecting tubule by combining with hydrogen to form water and carbon dioxide, which is then recombined to form new bicarbonate and reabsorbed. Hydrogen ions are excreted at the late distal tubule and collecting duct by combining carbon dioxide and water to form carbonic acid, which dissociates into hydrogen and bicarbonate ions, with the hydrogen then excreted in the urine. In high acid conditions, the kidneys conserve bicarbon