The digestive system provides two major functions, digestion and absorption. Foods must be digested in order for their nutrients to be absorbed. Saliva glands begin the digestive process at the sight and smell of food. After food enters the mouth and is moisten by saliva and chewed by the teeth, it transforms into bolus. Once the bolus leaves the mouth, it moves to the pharynx where it can be swallowed. The bolus then moves from the pharynx in to the esophagus, which connects the pharynx to the stomach. Once the bolus reaches the stomach it is mixed with acid secretions to transform the bolus into chime, which is a semiliquid food mass. Food is partially digested in the stomach, and chime empties in two to three hours depending on the size and type of food ingested.
The liver, gallbladder, and pancreas all contribute to the digestion process once the chime reaches the small intestine. The large majority of nutrient absorption from food takes place in the small intestine. The small intestine is divided in to three parts, duodenum, jejunum, and the ileum. Secretions of bile from the liver and gallbladder help with the digestion and absorption of fat, while the digestive enzymes and bicarbonate secretions from the pancreas aid in the digestive process. Materials not absorbed in the small intestine enter the large intestine through a sphincter, which keeps material from the large intestine from re-entering the small intestine. The large intestine is the colon and the rectum. Additional absorption of water and some vitamins and minerals occurs in the colon. Materials not absorbed in the colon are excreted from the body as waste products in the feces. The end of the colon is attached to the anus, which is the external
