Digestive Organs
Introduction
If I told you that you had a 20-foot-long hole in you, you would probably not believe it. But that precisely describes your gastrointestinal tract. From your mouth to your anus, a hole in your body exists that is covered by a mucous membrane, and uses muscles to move whatever you eat through a complex system of tubes in your body. The entire process, from chewing food to bowel movements, has been carefully crafted to extract nutrition and remove wastes. Each organ performs a specific task.
Three different salivary glands in the mouth mix with the food to create a bolus, a mass that can be swallowed and digested in the stomach. The stomach is lined with a special membrane that is tough enough to withstand digestive juices that literally dissolve the food you eat, whereas the linings of the intestines are designed to absorb nutrients that you need out of the food. Along the way, complex chemical reactions turn food into energy, and when the body no longer needs energy, it is stored in the form of fat for use when it is needed. It performs all of these tasks without you being aware of it, other than the occasional growl you may hear in a quiet room; but when something goes wrong, your digestive tract can literally rule your life.
Still, most people never experience anything but the occasional sick tummy, and the human digestive tract has evolved to deal with most of the problems. The stomach itself is a large opening in the tract guarded on both ends by sphincters, or valves, that isolate it from the rest of the tract. The stomach contains a caustic soup of digestive juices that can erode the linings of other organs such as the esophagus, the small intestine and the colon (or large intestine).
The pyloric sphincter, the valve between the stomach and the small intestine, controls the flow of digested food into the duodenum, where it is further digested by pancreatic enzymes and bile. In the small intestine, circular folds help to slow the movement of food from the stomach to the colon so nutrients can be absorbed into the body. In the large intestine, water is absorbed from the liquid material that passes from the small intestine into the colon creating feces that is stored in the rectum prior to a bowel movement. The digestion system is a wonder of chemicals, muscles and membranes, all working together in a very organized fashion to keep us alive.