These secretions contain digestive enzymes which speed up the process of hydrolysis, by which food is broken down by water. The Mouth Digestion begins in the mouth, where food is physically broken down and mixed with saliva before it is swallowed. Although dogs are not obligatory carnivores, their teeth are particularly suited to a meat-eating lifestyle and are capable of cutting, chewing and crushing food. Nevertheless, many dogs have a tendency to bolt their food and it is often only the toughest of foods which are chewed before swallowing. Once the food arrives in the mouth its taste and physical presence help to further increase saliva production.
Saliva contains mucus, a very effective lubricant, and coats the food to facilitate swallowing.
The stomach has several functions. Digestion of protein begins in the stomach. The major enzyme, pepsin, is secreted in an inactive form, pepsinogen, so as not to digest the cells which produce it. Pepsinogen is activated in the stomach in the presence of hydrochloric acid, which also creates the correct acid environment for the enzymes to function at their optimum rate. The secretion of acid, mucus and enzymes depends on the composition and quantity of food eaten and is regulated by both hormones and nerves.