The main purpose of the digestive system is to facilitate the utilization of food as sources of energy for the many bodily functions, and to supply the constituents necessary for the growth and the replacement of tissues. Since food is a combination of many substances, including sugars and starches, proteins, fats, minerals, and vitamins, the digestive tract must possess various mechanisms for dealing with the multiple constituents. The mouth plays an important initial role, in that food must be chewed thoroughly to divide the large, tough portions into smaller pieces for easier swallowing and digestion. The first step in the digestion of starches, such as potatoes, take place in the mouth, through the action of a specific substances (ptyalin) in the saliva, which digest starches. substances disintegrating large particles into small ones called enzymes. The digestive tract has many enzymes; digestion, in the strict scientific sense, therefore, signifies the breaking up of complex food into chemicals, so that the body may absorb them more readily; enzymes play a major role in this process. Once food has been chewed, the act of swallowing forces food into the esophagus which then sends it to the stomach. Food entering the stomach is acted upon powerful muscular action so that the material is further subdivided into smaller food particles. Little absorption of nutrients is absorbed by the stomach, food then passes to the small intestines, large intestines, and then the rectum.
The image above is that o f the digestive tract and their function.
PubMed:http://www.ncbi.nlm.nih.gov/pubmed/24650544
Sources: Fishbein, Morris. The New Illustrated Medical and Health Encyclopedia.
New York: H. S. Stuttman, 1970. Print.
New York: H. S. Stuttman, 1970. Print.