The digestive system of a dog is adapted to the diet of the species; it consists of the mouth including the teeth, jaws and saliva, and the gastrointestinal tract, which includes the pharynx, esophagus, stomach, small and large intestines, colon, pancreas, gall bladder and liver. The dog is largely carnivorous and this makes its digestive system different from omnivorous humans. The dog’s system is also shorter than a human, to make it possible for the protein in the food to be processed faster.
Jaws, Teeth and Saliva
The dog has powerful jaws that work like a hinge for gripping its food. The teeth are suited to eating meat, with small teeth at the front for nibbling or scraping meat off a bone. The incisors on either side cut through the meat to bite off chunks, and the back teeth are used to crush the food before swallowing. The dog does not chew; rather, the saliva provides lubrication to help the food move through the dog’s system.
The pharynx and esophagus are the pathways to the dog’s stomach. As the food leaves the mouth, it first enters the pharynx and then the esophagus, which carries it through the chest to the stomach. A tight sphincter muscle at the entrance to the stomach ensures that once the food passes through it cannot return easily and prevents stomach acid from moving back up the esophagus.
The food is stored in the stomach for a short period while it is dissolved and broken down for digestion. During this time proteins are drawn from the food for absorption into the dog’s system and then the food passes into the small intestine.
While the food is in the small intestine, it is broken down into even smaller particles that can be absorbed into the blood. In this stage the majority of the nutrients are absorbed, along with water and electrolytes. The processed food then passes into the large intestine, where the last water and electrolytes are extracted and the remainder is turned into feces. While in the large intestine, enzymes that produce bacteria break down any material that is difficult to digest.
The pancreas and gall bladder help in the digestion of food by releasing enzymes and bile into the small intestine. The enzymes help to break down proteins and regulate blood sugar, while the bile serves to break down fats. The liver acts as a storage area for the nutrients and proteins that are delivered to it by the blood. Dogs are one of a very few species with livers that can regenerate lost or damaged tissue without help. The liver also helps to remove potentially harmful toxins from the blood and eliminate them from the system.