The importance of the digestive system stems from the fact that the food that we ingest is digested and absorbed there into the blood circulation. It is theoretically possible to live without the digestive system and receive all necessary nutrients intravenously. However this would be a very unusual situation.
In malignancy of the gastrointestinal tract the risk does not follow the tumour itself but instead the metastases to lymph nodes and to other organs which can form the ultimate complications to the original tumour. Malignancy of the digestive system can be treated with surgical removal of the affected part and the cure is 100% as long as there is no metastases to other parts of the body.
The digestive system system is comprised of the esophagus which is a muscular tube that functions as a passage way for ingested food that enter the stomach by passing through the esophagus.
The esophagus does not have any apparent role in the digestion process of food but instead it contains mucous secreting cells which secrete mucus that help in lubricating the inner surface of the esophagus a process which facilitates the propulsion of food through the canal.
The esophagus is connected with the stomach using the gastroesophageal sphincter which is a one way valve that makes sure the food in the stomach does not reflux to the lower part of the esophagus.
In certain medical conditions such as when administering drugs that relax smooth muscles, reflux of food from the stomach to the esophagus occurs. A process which causes a condition that is called reflux esophagitis.
In the stomach, the food is partially digested. In particular the proteins in the food are degraded using an enzyme that is called pepsin which is secreted by the stomach epithelial cells that secrete also acidic juice that helps in the digesting process and which is called gastric juice. The stomach is connected with the small intestine through the gastroduodenal sphincter which functions as a barrier to backflow of duodenal contents to the stomach.
The duodenum is the first part of the small intestine which is a long tube that includes, in addition to the duodenum, other anatomical structures that are called the jejunum and the ileum. The duodenal contents are basic in pH due to the secretion of bicarbonate ions from the pancreas and from bile through the ampulla of vater which is a joint openning to contents from the pancreas and the gallbladder.
Most of the absorption of nutrients occurs in the small intestine. The epithelium of the small intestine is composed of microvilli which have high surface area that makes the absorption process of food very eficient. In malabsorption diseases the small intestine is mostly affected due to its major role in food absorption.
The small intestine is connected with the large intestine or colon through the ileocecal valve which functions as a barrier to backflow of of food from the colon to the ileum. In addition it makes sure that food is propelled in a one way direction. The large intestine or colon is less important than the small intestine as far as absorption is concerned.
It secretes mucus that helps propelling food through the colon. The colon has a role in adsorption of water and electrolytes. The ascending colon or left side of the large intestine is wider in diameter that the right side or the descending colon. This is important clinically in distinguishing between malignancies of the colon, whether it originates in the right side or the left side.
Due to the wider diameter of the right colon and due to its semiliquid content cancer in this area is not likely to cause constipation in contrast to cancer in the left side which can cause constipation due to its lower diameter.