The digestive system is composed of the digestive or alimentary tube and accessory digestive organs. The basic terminology used to describe parts of the digestive system is shown below and more detailed description of each is presented in later sections.
The digestive system depicted above - a carnivore - is the simplist among mammals. Other species, even humans, have a more or very much more extensive large intestine, and ruminants like cattle and sheep have a large set of forestomachs through which food passes before it reaches the stomach.
Each of the organs shown above contributes to the digestive process in several unique ways. If you were to describe their most important or predominant function, and summarize shamelessly, the list would look something like this:
- Mouth: Foodstuffs are broken down mechanically by chewing and saliva is added as a lubricant. In some species, saliva contains amylase, an enzyme that digests starch.
- Esophagus: A simple conduit between the mouth and stomach - clearly important but only marginally interesting compared to other regions of the tube.
- Stomach: Where the real action begins - enzymatic digestion of proteins initiated and foodstuffs reduced to liquid form.
- Liver: The center of metabolic activity in the body - its major role in the digestive process is to provide bile salts to the small intestine, which are critical for digestion and absorption of fats.
- Pancreas: Important roles as both an endocrine and exocrine organ - provides a potent mixture of digestive enzymes to the small intestine which are critical for digestion of fats, carbohydrates and protein.
- Small Intestine: The most exciting place to be in the entire digestive system - this is where the final stages of chemical enzymatic digestion occur and where almost almost all nutrients are absorbed.
- Large Intestine: Major differences among species in extent and importance - in all animals water is absorbed, bacterial fermentation takes place and feces are formed. In carnivores, that's about the extent of it, but in herbivores like the horse, the large intestine is huge and of critical importance for utilization of cellulose.