Gastrointestinal System
The gastrointestinal system includes structures that form the alimentary canal and the accessory organs of digestion. Digestion breaks down large compounds in food and liquids into smaller molecules that can be absorbed into the bloodstream. The absorbed nutrients include carbohydrates, proteins, fats, minerals and vitamins. They are processed, then delivered throughout the body and used for energy, growth and cell repair.
The alimentary canal is one continuous tube that includes - in order-the oral cavity, pharynx, esophagus, stomach and intestines. When food enters the mouth, it is pushed down the esophagus, travels to the stomach and finally to the intestines. Each of these structures plays its own important role in digestion.
The autonomic nervous system controls peristalsis -contraction and relaxation of muscles layers within the alimentary canal wall. Peristalsis is a key function is digestion, it literally gets the ball rolling. These involuntary contractions push swallowed food down the esophagus, churn the stomach, and propel chyme through the small intestine and large intestine.
The digestive system can be subdivided into six main categories:
Ingestion - food is ingested, chewed and swallowed
Propulsion - muscular contractions propel the swallowed food through the alimentary canal
Mechanical breakdown - the food is physically broken broken down into smaller parts during the above steps
Chemical digestion - digestive fluids chemically break down the nutrients from food into small molecules
Absorption - the small molecules are absorbed into the blood stream
Elimination - indigestible and unabsorbable substances are eliminated as waste.