Despite its diminutive name, the small intestine is actually the longest part of the digestive tract, stretching some 22 feet in length. The large intestine, however, is just five feet long. The names, small and large intestine, refer to their width, not their length.

When full, the stomach holds between a quart and a quart and a half of food and liquids. And it takes about four hours for the stomach to fully digest a meal and pass it along to the small intestine. Food passes through the small intestine in just four hours, zipping along at more than a half an inch per second. Inside the large intestine, it takes about eight to 15 hours, traveling at a more leisurely rate.

The inside of the small intestine, which absorbs the digested proteins, sugars and fats from food, is covered with a furlike layer of tiny projections called villi and microvilli. This food-absorbing "fur" boosts the surface area by 600 to 1,000 times, compared to what a smooth interior surface would provide. If the interior of the small intestine were smooth, it would have to be more than 1 mile long to provide the same food-absorbing power as its present 22 feet.

Each day, about three gallons of food, liquids and digestive juices gurgle through the digestive tract. Only about half a cup emerges as feces.