stomach
The definitions used in this glossary of terminology either have been provided by the authors of the articles, or have been extracted wholly or in part, or paraphrased from the following sources: The American Medical Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d Edition, William Bains, Oxford University Press, New York, New York, 2002; A Dictionary of Genetics, 6th Edition, Robert C. King and William D. Stansfield, Oxford University Press, New York, New York, 2002; Dorland's Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford University Press, New York, New York, 2000; The Gale Encyclopedia of Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson Learning, New York, New York, 2002; The Merriam-Webster Dictionary, Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland Publishing, 1994; The Random House Dictionary of the English Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate Dictionary, 1991.
DEFINITION:
- stomach
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A hollow, saclike organ of the digestive system that is connected to the esophagus and the duodenum (the first part of the small intestine). The stomach lies in the left side of the abdomen under the diaphragm.
STRUCTURE:
The stomach is flexible, allowing it to expand when food is eaten; in an adult, the average capacity is about 3 pints (1.5 liters). The stomach wall consists of layers of longitudinal and circular muscle, lined by special glandular cells that secrete gastric juice, and supplied by blood vessels and nerves. A strong muscle at the lower end of the stomach forms a ring called the pyloric sphincter that can close the outlet leading to the duodenum.
FUNCTION:
Although the main function of the stomach is to continue the breakdown of food that is started in the mouth and completed in the small intestine, it also acts as a storage organ, enabling food to be eaten only two or three times a day. Food would have to be eaten every 20 minutes or so if storage were not possible.
The sight and smell of food and the arrival of food in the stomach stimulate gastric secretion. The gastric juice secreted from the stomach lining contains pepsin (an enzyme that breaks down protein), hydrochloric acid (which kills bacteria taken in with the food and which creates the most suitable environment for the pepsin to work in), and intrinsic factor (which is essential for the absorption of vitamin B12 in the small intestine). The stomach lining also contains glands that secrete mucus, which helps provide a barrier to prevent the stomach from digesting itself.
The layers of muscle produce rhythmic contractions about every 20 seconds that churn the food and gastric juice; the combined effect of this movement and the action of the digestive juice convert the semisolid food into a creamy fluid. This process takes varying lengths of time, depending on the nature of the food. Generally, however, the richer the meal, the longer it takes to be emptied from the stomach. The partially digested food is squirted into the duodenum at regular intervals by the contractions of the stomach and relaxation of the pyloric sphincter.
DISORDERS:
Disorders of the stomach have a variety of causes. Because the stomach is a reservoir, disorders in the process of emptying the stomach contents occur. Other problems relate to the stomach's role in the preparation of ingested food for digestion.
Some of the disorders which may occur are infection, tumors, ulceration, autoimmune disorders, and twisting or enlargement of the stomach.
Used in 2 Article abstracts
Used in 2 Article abstracts