ABSTRACT
Saliva is secreted by acinar cells, which make up units called salivons. On secretion it is isotonic to plasma. It then undergoes secondary modification in the intercalated and excretory ducts. Na+ is actively reabsorbed and Cl− is passively taken up with it. K+ and HCO3− are actively secreted into the ducts. Saliva therefore reaches the end of the duct, hypotonic to plasma (200 mosmol/L) and alkaline.
