A dog digestive system is different than a human's and therefore dogs process and eat differently than us. This is important to know and understand so that you can feed your dog the correct diet and be aware when something goes wrong.
The Mouth
In humans, the role of the mouth, teeth and saliva play an important part in the digestion of food. In canines, this is not true. Dogs' mouths are designed to bite off and chew large pieces and to eat quickly. Dogs have hinged jaws and large teeth, meant to ingest large chunks of meat, bones and fat products that are usually a part of the dog diet.
Esophagus to Stomach
Since the mouth is not really a part of the digestive process, per se, the stomach is really more vital to the digestion of a dog's food. The food passes through the esophagus on its way to the stomach.
Once food reaches the dog stomach it is processed with a high level of hydrochloric acid. This is important because this allows the breakdown of the large pieces of protein and bones that dogs ingest. Dogs also have a natural regurgitation instinct which allows them to spit out food that has not been processed correctly, then to re-swallow it.
Stomach to Small Intestine
After food has been processed in the stomach with the aid of the hydrochloric acid, it then passes through to the small intestine in the form of liquid. This is where the main part of the digestion occurs and where the food is assimilated into nutrients for the dog body.
Small Intestine to Large Intestine
From the small intestine, the unassimilated food passes through to the large intestine. The large intestine is the last stop before the waste is passed through rectum in the form of feces.
Other Considerations
The dog actually has the shortest digestive system of mammals and it takes roughly 8-9 hours for the whole digestive process. Of course, that number is smaller for puppies, which do not have the mature system of adolescent and adult dogs.
The digestive system of canines is important and can be a good indicator when something is not working correctly or when illness is present. You should be familiar with your dog's eating habits and pooping habits as well. If your dog is acting out of sorts, has dog bloat, or is not eating or pooping as usual, there is probably something going on inside.
Although most dogs experience some gas, just as humans do, particularly unpleasant gas is usually an indication of a poor diet. This can cause other problems so be consistent with your dog's diet and feeding habits.