Todd Morris, age 13, of Nashua, N.H., for his question:

HOW LONG IS A PERSON'S COLON?

The colon is part of the large intestine. This muscular tube carries food residue from the cecum, or first part of the large intestine, to the rectum, which is the last part. A person's colon is about five feet long.

A person's small intestine, by the way, is about 20 feet long.

There are four sections of the colon. The ascending colon extends upward on the right side of the abdominal cavity. It joins the transverse colon, which extends across the cavity to the opposite side. This section meets the descending colon, which passes down the left side to join the S shaped sigmoid colon.

The colon removes water and mineral salts from the food residue, which is called chyme. The colon's strong muscles contract and relax to push the chyme toward the rectum.

Mucus covers the colon's inner surfaces to lubricate them and to ease the passage of the residue.