Human digestive system
Chewing, in which food is mixed with saliva, begins the mechanical process of digestion. This produces a bolus which can be swallowed down the esophagus to enter the stomach. Here it is mixed with gastric acid until it passes into the duodenum where it is mixed with a number of enzymes produced by the pancreas. Saliva also contains a catalytic enzyme called amylase which starts to act on food in the mouth. Another digestive enzyme called lingual lipase is secreted by some of the lingual papillae on the tongue and also from serous glands in the main salivary glands. Digestion is helped by the chewing of food carried out by the muscles of mastication, by the teeth, and also by the contractions of peristalsis, and segmentation. Gastric acid, and the production of mucus in the stomach, are essential for the continuation of digestion.
Cat anatomy
Food moves from the stomach into the small intestine. The first part of the small intestine is the duodenum. As food moves through the duodenum, it mixes with bile, a fluid that neutralizes stomach acid and emulsifies fat. The pancreas releases enzymes that aid in digestion so that nutrients can be broken down and pass through the intestinal mucosa into the blood and travel to the rest of the body. The pancreas doesn't produce starch processing enzymes because cats don't eat a diet high in carbohydrates. Since the cat digests low amounts of glucose, the pancreas uses amino acids to trigger insulin release instead.