the acidic environment quickly inactivates the amylase. Enzymatic digestion of proteins begins in the stomach. The gastric glands of the mucosa of the stomach wall secrete pepsin which functions under the very acidic conditions produced by the hydrochloric acid the stomach lining also secretes. Yet pepsin does not hydrolyze proteins completely into individual amino acids but splits only a few select peptide bonds.
Most enzymatic digestion of sugars and proteins and all the breakdown of fats occurs in the small intestine. When the stomach contents enter the small intestine, the acidity stimulates the pancreas and intestinal glands to secrete their digestive enzymes. The pancreas, which is connected to the small intestine by the pancreatic duct, secretes two digestive enzymes, pancreatic amylase and lipase. Pancreatic amylase breaks starches into double sugars. Despite the fact that lipase is the principal fat-digesting enzyme, it is able to hydrolyze only a small percentage of the fats present in food into fatty acids and glycerol. Fat can be absorbed across cell membranes
