Which of the following mechanisms is/are used by the kidneys to regulate the pH of the blood? Circle all that apply.

a. Hydrogen ions are secreted from the proximal and distal tubules and the collecting system.

b. Hydrogen ions are reabsorbed from the nephron loop.

c. New bicarbonate ions are formed from glutamine and carbon dioxide in the interstitial fluid that enters proximal tubule cells.

d. Bicarbonate ions can be secreted.

e. Bicarbonate ions are reabsorbed directly from the filtrate.