Vance Forbes, age 14, of Marquette, Mich., for his question:
HOW LONG DOES FOOD STAY IN YOUR STOMACH?
Between the esophagus and the small intestine is an enlarged part of the alimentary canal called the stomach. The stomach serves as a storage place for food, so that a large meal may be eaten all at one time. The stomach also helps to digest food.
The length of time that the stomach retains food after a meal has been eaten varies. With the mixed diet of most people, the stomach empties in three to five hours.
Glands in the stomach wall secrete mucus to lubricate the food that has been eaten. Other glands give off hydrochloric acid and the enzyme pepsin to partially digest the food.
The stomach muscles churn the food and digestive juices into a pulpy liquid. Then the muscles squeeze the liquid toward the pyloric, or intestinal, end of the stomach by ringlike contractions of the muscles.
These contractions, called peristaltic waves, occur about 20 seconds apart. They start at the top of the stomach and move downward. The pylorus, a ringlike muscle around the duodenal opening, keeps food in the stomach until it is a liquid. Then the pylorus relaxes and lets some of the liquid digested food, called chyme, pass into the duodenum.
The churning action of the stomach tends to start at our usual mealtimes. When a person says his stomach is growling, he is referring to these peristaltic waves. Sometimes these movements grow so strong that they squeeze acidic gastric juices up into the lower part of the esophagus. This irritates the tissues there and causes discomfort.
The pylorus allows water to pass through almost as soon as it enters the stomach, but the food must remain for up to five hours.
When food enters the stomach, it contains ptyalin, an enzyme in saliva that partially digests starch. This action is stopped immediately by the hydrochloric acid in the stomach. No further digestion of starch occurs until the chyme enters the small intestine.
For this reason, salivary ptyalin is not too important for digestion.
Although the stomach performs several useful functions, it is not absolutely essential for life. Many persons lead long lives after their stomachs are either partially or wholly removed because of ulcers or cancer.
Many foods irritate the mucous membrane that lines the stomach. Included are highly spiced foods, extremely hot foods and some alcoholic foods or drinks. Rough food that is not well chewed can also irritate the stomach.
Fear, anger or constant tension can cause an excessive secretion of stomach juices even when no food is present. This greatly irritates the stomach and the duodenum. If made worse by hastily eaten coarse food, a person can develop ulcers in the stomach or duodenum.