which substance functions to control the release of hydrochloric acid to prevent excessive acidity?

Solution:

A compound consisting of hydrogen and chlorine. Hydrochloric acid is secreted in the stomach and is a major component of gastric juice. A clear, colorless, fuming, poisonous, highly acidic aqueous solution of hydrogen chloride, HCl,it is a chemical intermediate used in, food processing, pickling, and metal cleaning. It is found in the stomach in dilute form. HCI is Hydrogen (H), Carbon (C) and Iodine (I). Although,  

HCI is not balanced, so, that would actually be an ion, with negative charge.a hormone that stimulates secretion of gastric juice, and is secreted into the bloodstream by the stomach wall in response to the presence of food.

thus for controlling  Gastrin is used.

Gastrin is a peptide hormone that stimulates secretion of gastric juice (HCl) by the partial cell of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach.

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.