Digestive System

This system processes food into absorbable units and eliminates indigestible wastes, by taking in food, breaking it down into nutrient molecules, absorbing these molecules into the bloodstream, and then ridding the body of the indigestible remains.



The digestive tract can be viewed as a "disassembly line" in which food becoems less complex at each step of processing.

The digestive system involves 6 essential activities:

1. Ingestion- taking food into the digestive tract via the mouth.
2. Propulsion- food moves through the alimentary canal, includes swallowing, which is initiated voluntairly.
3. Mechanical digestion- physically prepares food for (chemical) digestion by enzymes, this includes chewing, using tongue to mix food and saliva, churning food in the stomach, and mixes the food with digestive juices. It increases the efficiency of absorption by repeatedly moving the food mass over the intestinal wall.
4. Chemical digestion- complex food molecules are broken down to their chemical building blocks.
5. Absorption- a mixture of digested end products with vitamins, minerals and water from the GI tract through mucosal cells by active transport into blood or lymph.
6. Defecation- ridding the body of indigestible substances in the form of feces from the anus.

• The small intestine is the major absorption site.
• A muscle called peristalsis pushes the food down to the esophagus.
• The small intestine is 3 grown men tall and 2 fingers wide.
• A typical person harbors more than 400 distinct species of bacteria within the colon.

http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/