Gastric juice is a clear, colorless fluid secreted by specialized cells in the fundus of the stomach. It contains hydrochloric acid, pepsinogen (an inactive proenzyme that is converted to pepsin), mucus, and intrinsic factor. An average of 1.5 quarts (a little less than 1.5 liters) of gastric juice is secreted daily. The major function of gastric juice is to digest protein. The acidity of gastric juice denatures proteins and inactivates most of the enzymes in food. The acidity of gastric juice creates an environment that is unfriendly to many microorganisms ingested with food that may be harmful.