Louie Valdivia, age 13, of Los Angeles, Calif., for his question:

How does the body digest food?

We have some say in choosing, chewing and swallowing our food. But the big ,job of digestion is done automatically by the digestive tact or alimentary canal   without any help from our conscious minds. The canal is really a long pipe with a series of chambers and anterooms called the organs of digestion. These organs include the stomach, the liver and the pancreas. Each plays a part in breaking our food down into simple molecules which can be dissolved in liquid form and absorbed by the blood.

The food passes from the mouth down a tube called the esophagus into the stomach. From there it passes through another tube called the duodenum into the small intestine. It is passed along by a wave like motion of the muscles called peristalsis. This movement also pummels and churns up the food to mix it with liquids and various digestive juices. The digestive tract uses 10 to 15 quarts of liquids every day. Some of this liquid is contained in the foods we eat. The body gets the rest of it from the water and other liquids we drink   and the best time to drink water is between meals.

Digestion actually begins in the mouth. The food is chomped up and mixed with liquid saliva, which is actually a digestive juice. It breaks down starches into simple sugar. If you chew a savory, starchy soda cracker and keep it in your mouth for a little while., it becomes sweet to the taste. The saliva has broken down some of the starch into sugar.

Each mouthful of chewed food then passes down the esophagus into the stomach.

Pints of liquid hydrochloric acid containing digestive enzymes are poured in from the linings of the stomach walls.  Peristalsis pounds, pummels and (nixes the food with these digestive juices. The meaty proteins in the original food begin to change into molecules of amino acids. The buttery fats begin to change into fatty acids and the starchy carbohydrates start turning into sugars. The soupy mixture from the stomach is passed down the duodenum tube where more digestive juices are added. Pancreatic ,juice comes in through a duct which connects with the pancreas. This vial fluid digests all types of food. Bile pours in through a duct which connects with the liver. Bile digests fats. The food., now almost digested, passes down into the small intestine, an amazing tube maybe 21 feet long. Here more liquid is added through the intestine walls. The original food is now in the form of molecules which the body cells can absorb. It is in liquid form, for this is how the blood can absorb and carry it to build and repair where it is needed.

When it reaches the upper intestine, the food is properly digested. Meat, milk, carrots and everything on the menu have been reduced to simple chemicals, dissolved in soupy liquid. Tiny blood vessels, millions of them, come very close to the surface of the small intestine walls, The digested food passes through the thin cell walls into the blood stream.