CO 2 levels are controlled by the lungs by breathing. Proximal tubule cells are impermeable to bicarbonate on the tubule side. Thus bicarbonate enters across cell walls in the form of carbon dioxide. Bicarbonate leaves for the blood side as bicarbonate, while proton either goes into the filtrate or into the blood.
Chemical buffers bind protons.
Organisms immediately increase ventilation to blow off carbon dioxide. Organisms begin to increase secretion and excretion of protons via the urine thereby decreasing plasma protons. Organisms reabsorb all filtered bicarbonate from the kidney tubules and add new bicarbonate to the plasma thereby increasing plasma bicarbonate. Chemical buffers release protons. Organisms immediately decrease ventilation to retain carbon dioxide.