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.
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