Hormones stimulate enzyme release. Mechanical breakdown of food and its mixing with saliva begin in the mouth. Teeth chew the food. Saliva contains salivary amylase to begin carbohydrate digestion, bicarbonate to neutralize acids, and mucins to lubricate. The stomach is a muscular sack that stores and mixes food, secretes substances to dissolve and degrade food, and controls the rate at which food enters the small intestine.
Gastric fluid includes hydrochloric acid, pepsinogens, and mucus.
The Small Intestine a. Digestion is completed and most nutrients absorbed in the small intestine. Enzymes act on all the macromolecules of food. Bicarbonate buffers the acid from the stomach.