Stomach
The stomach is a funnel-shaped organ located under the diaphragm, between the liver and the spleen. The stomach is made up of a number of tissue layers among which is a layer of muscle which acts to move food around.
The innermost layer is the mucous membrane, which produces and secretes mucus, hydrochloric acid, and enzymes. The mucus is constantly secreted from the walls of the stomach, thus protecting the stomach from being digested by its own enzymes and acid. The acid kills bacteria which can be mixed with the food. The enzymes secreted require a low pH to function, and are responsible for the digestion of protein. The stomach also produces a substance essential in the absorption of vitamin B-12.
The food enters the stomach by passing through the esophagus into the cardia. It then passes to the fundus, the upper portion of the stomach, from where it passes out of the stomach through the pyloric sphincter which opens to the duodenum. Food can stay in the stomach for long periods of time. The time needed to digest the food depends on its particular characteristics. Bread can be digested in two to three hours; sardines in oil can take eight to nine hours.
References
Crafts, R.C. 1985. A Textbook of Human Anatomy. John Wiley and Sons, Inc. New York. 906 pp.
Gray, H. 1977. Gray's Anatomy. Crown Publishers, Inc. New York. 1257 pp.
Lockhart, R. D., G. F. Hamilton, et. al. 1974. Anatomy of The Human Body. Faber and Faber Limited. London. 697 pp.
Van Amerongen, C. The Way Things Work - Book Of The Body. New York: Simon and Schuster, 1979.
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