As you chew your food and swallow, the food travels through your esophagus -- which is the passageway that connects your mouth to your stomach. In the stomach, strong acids and enzymes digest, or break down, the food into small particles. Some of these particles are probably familiar to you. They are called proteins, fats, and carbohydrates.

After leaving your stomach, these food particles enter the small intestine. This is a long, continuous tube that slowly contracts, or squeezes, to push the food along through it. As the small intestine continues to digest your food, it absorbs nutrients that your body uses for energy, growth, and repairs. By the time the food reaches the end of the small intestine, almost all of its nutrients have been absorbed. At this point, what's left of the food is mostly water and indigestible waste products.

This material then enters the large intestine, or colon, which is also a long tube. Its main job is to remove water from the waste products as they pass through and recycle this water back to your body.

After traveling through this area, the waste is held at the end of the colon in the rectum. It will then leave your body through the anus as stool when you have a bowel movement. How firm your stool will be depends on how long it has been in your colon. If the stool moves through quickly, it will be more watery. But if it moves through too slowly, you can become constipated. This is because the longer stool stays in the colon, the more water is removed from it.

The walls of your digestive tract are made up of four layers of tissue. The innermost layer is a lining made of cells that are shed and replaced regularly in a healthy body. This lining can have different functions in different parts of the digestive tract. For example, the lining in the small intestine releases water and digestive enzymes, and it absorbs nutrients from the food you eat.

This lining also releases mucus throughout nearly the entire length of the digestive tract. This mucus does two things to help digestion:

• It helps protect the digestive tract from being damaged by the harsh digestive juices
• It lubricates the inside of the tract so that solids can pass through more easily.

If the lining or other layers of tissue in your digestive tract are infected, inflamed, or otherwise damaged, it can cause several problems.