John Ikerd, age 10, of Visalia, Calif., for his question:
WHAT IS THE DUODENUM?
A long tube through which food is taken into the human body and digested is called the alimentary canal. It is a passage that is about 30 feet long. Animals that eat meat usually have shorter alimentary canals than animals that eat grass. In man, food starts its trip through the alimentary canal as soon as it enters the mouth and is swallowed.
As soon as you swallow food, the muscles of your pharynx push the food into your esophagus. Muscles in the esophagus wall contract in a rhythm to move the food down to the stomach.
In the stomach, fluids lubricate and partially digest the food. Contractions of the stomach move the food into the small intestine. The first section of the small intestine is called the duodenum.
The small intestine is the longest section of the body's alimentary canal. It twists and coils for more than 20 feet. The duodenum is about 10 or 11 inches long.
The duodenum received its name from the Latin for "twelve," owing to the fact that its span was originally measured by finger widths instead of by inches. In the duodenum, the hydrochloric acid in the food arriving from the stomach is neutralized by alkaline digestive juices.
Some of the alkaline digestive juices in the duodenum come from the pancreas, a soft, pink gland which lies below and behind the stomach. Some of it comes from the liver, the heaviest organ in the body, which is a dark red gland situated below the lower right side of the rib cage.
With the acid neutralized, the chemical breakdown of food moves into high gear. As the food is forced along the duodenum, it undergoes constant bombardment by the most powerful of all the digestive enzymes.
A man whose stomach has been removed by surgery can still satisfactorily digest his food if it is properly chewed. But the stoppage of enzymatic action in the duodenum could be critical.
The opening between the stomach and the duodenum is called the pylorus. This is a ringlike muscle which keeps food in the stomach until it is a liquid.
When the phylorus relaxes, it lets some of the liquid digested food called chyme pass into the duodenum.
The enzymes secreted in the stomach are called pepsin, which partially digests proteins and clots milk, and rennin, which also clots milk. Fat digestion occurs in the small intestine.