Timothy Harteau, age 13, of Pocatello, Ida., for his question:

WHAT HAPPENS IN THE ILEUM?

The ileum is the lower two thirds of the small intestine in your body. The small intestine and the ileum form a muscular tube used for digesting and absorbing the major portion of our food.

When food is being digested, it moves through the ileum by means of muscular action.

The intestinal wall is lined with tiny projections called villi. These tiny projections increase the ileum's power to absorb wate, salt and other acids during digestion.

The mucous membrane lining of the intestinal wall has many circular folds called plicae. They delay the food so that it may be absorbed and digested as it passes through the intestine.

The folds of the mucous membrane work like spoons and actually mix the food. The food is almost fully digested when it reaches the lower end of the ileum.

The ileum is attached to the abdominal wall by the mesentery, which contains blood vessels and nerves.