Structure:
The digestive tract begins in the mouth and pharynx, and goes through the
esophagus, stomach, the small intestines (duodenum, jejunum, and ileum),
the large intestine, also called the colon, the rectum, and ending at the
anus. The liver, gall bladder, and pancreas contribute the bile and digestive
enzymes for the digestion of food. The Islets of Langerhan in the pancreas
are part of the endocrine system.
Function:
Ingesting food, chewing, beginning digestion with saliva, and swallowing
are the voluntary parts of digestion. Once food is swallowed food is further
digested involuntarily in the stomach by acid and gastric enzymes. Then,
the food enters the small intestine where it is met by liver bile and pancreatic
enzymes to assist digestion. Food is propelled forward by the smooth
muscle of the intestines, and undigested food residues and bacteria
are expelled as feces. The metabolic products of digestion are absorbed
through the intestinal walls into the lymphatic
capillaries, and enter the circulation
through the thoracic ducts. The primary purpose of digestion is the production
of energy. The ileum and the appendix have patches
of lymphoid cells that are part of the lymphatic
system.
