<prompt> Which of the following ion is exchanged in the stomach for H secretion?NaKCaCl-  <response>: The unique characteristic of gastric secretion is its high concentration of hydrochloric acid, a product of the parietal cells. As the concentration of H rises during secretion, that of Na drops in a reciprocal fashion. K remains relatively constant at 5-10 meqL. Chloride concentration remains near 150 meqL, and gastric juice maintains its isotonicity at varying secretory rates. Acid secretion at the apical membrane is accomplished by a membrane-bound HK-ATPase the proton pump; H is secreted into the lumen in exchange for K. Ref: Dohey G.M., Way L.W. 2010. Chapter 23. Stomach Duodenum. In G.M. Dohey Ed, CURRENT Diagnosis Treatment: Surgery, 13e. 