Sheri Walters, age 10 of Richmond Va., for her question:

WHY DOES YOUR STOMACH GROWL?

When your stomach makes a noise that sounds like a growl or a rumble, it is usually the churning action the stomach tends to start when your usual mealtimes arrive. The stomach action comes in peristaltic waves.

Stomach muscles actually churn the food and digestive juices in your stomach 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 ringlike contractions are called peristaltic waves. The waves occur about 20 seconds apart and 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 liquid.

Once the material in your stomach has been turned into a liquid, the pylorus relaxes and lets some chyme, as liquid digested food is called, pass into the duodenum. This action can also sometimes produce a growling sound that you can hear.

The stomach's pylorus will allow water to pass through almost as soon as it enters the stomach. But the length of time that the stomach retains food varies. On the mixed diet that most persons eat, the stomach empties in three to five hours.

When food first enters the stomach, it contains ptyalin, an enzyme picked up in the saliva that partially digests starch. This action is stopped immediately by the hydrochloric acid in the stomach. No further digestion of starches occurs until the chyme enters the small intestine.

Pepsin and rennin are enzymes secreted in the stomach. Pepsin partially digests proteins and clots milk while rennin clots milk.

Babies have an enzyme called gastric lipase that digests fat in the stomach. In adults, fat digestion takes place in the small intestine.

The stomach's main job is to serve as a storage spot so that a large meal can be eaten at one time.

Did you know that the stomach isn't absolutely necessary or essential for life? Many persons lead long lives after their stomachs are either partially or wholly removed because of cancer or ulcers.

Sometimes highly spiced or extremely hot foods can irritate the stomach. Rough and dry food that is not well chewed can also irritate it.

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.

Duodenal ulcers almost always result from too much secretion in the stomach.