Complex sentence: Polystyrene sulfonates release sodium or calcium ions in the stomach in exchange for hydrogen ions, when the resin reaches the large intestine the hydrogen ions are exchanged for free potassium ions; the resin is then eliminated in the feces.
Split into simpler sentences: Polystyrene sulfonates release sodium or calcium ions in the stomach in exchange for hydrogen ions. When the resin reaches the large intestine the hydrogen ions are exchanged for free potassium ions; the resin is then eliminated in the feces.