All systems are go!

Diving into a tasty holiday meal is such a simple pleasure. It’s what happens to that delicious food after we taste it that is a lot more complicated. Every time we take a bite, that morsel of food takes a complex trip through the digestive system, a trip that is necessary in order to turn the food we eat into the food that gives us nourishment.

Even though we don’t think about it much until something goes wrong, “it is an active process to push food through your gut,” says Ravikant Varanasi, M.D., a gastroenterologist with Pinehurst Medical Clinic.

That active process is called digestion.

What is digestion?
Our diets are made up of foods that consist of nutrients—vitamins, minerals, carbohydrates, proteins and fats—residues such as fiber, and water. Most vitamins and minerals are absorbed into the bloodstream without change; however, the other nutrients are not in a form that the body can use for nourishment. These nutrients have to be broken down into simpler substances with smaller molecules in order to be absorbed into the blood and carried to the cells.

Digestion is the process that occurs to break food or drink down in their smallest parts so the body can use them.

“Your digestive system actually starts with your eyes and nose,” says Debra Deschamps, R.D., a nutritionist with the FirstHealth Diabetes Self-Management Program. “You see and smell food, which makes you salivate, and enzymes are released to initiate the digestion process before you even put food in your mouth.”

In a healthy digestive system, Deschamps says, the whole process of digestion takes an average of four hours.

The players involved
Several organs make up the digestive system. First is the digestive tract, which includes the mouth; pharynx (throat); esophagus; stomach; small intestine (duodenum, jejunum and ileum); large intestine (cecum, colon and rectum); and the anus.

This series of hollow organs is joined in a long, twisting tube that food passes through from the mouth to the anus.

The organs within the digestive tract contain muscle that enables their walls to move and propel food and liquid, and mix the contents within each organ. This movement of the esophagus, stomach and intestine is called peristalsis.

The digestive tract is not the only player involved in the digestion process. Two solid organs—the liver and the pancreas—produce digestive juices that reach the intestine through small tubes. The salivary glands in our mouths also produce digestive juices. Digestion starts in the mouth as we chew and swallow, and it is completed in the small intestine.

From the mouth to … well, you know
Let’s take a simple food like bread. You’ve smelled the fresh-baked bread, so you are already releasing those enzymes to start the digestion process. You take a bite and begin the physical act of chewing.

“Food is chewed into smaller pieces as it is mixed with saliva,” Deschamps says. “A complex carbohydrate like starch is released from the bread, and an enzyme called amylase starts to break it down.”

The first major muscle movement happens when you swallow the bread, a voluntary action. But once the swallow begins, the rest of the digestion process is involuntary and is commanded by our nerves.

“The bread and saliva mix is swallowed down the esophagus,” Deschamps says.

Digestion is the process that occurs to break food or drink down in their smallest parts so the body can use them.

The esophagus pushes the food downward with a series of wavelike contractions called peristalsis until it reaches the lower esophageal sphincter valve (LES).

“LES is a circular muscle that keeps the foods that enter the stomach from backing up into the esophagus,” Deschamps says.

The muscle is located at the junction of the esophagus and the stomach. As the food approaches the closed ring, the surrounding muscles relax and allow the food to enter the stomach, which has an important job to do.

“The stomach breaks down the food both chemically and physically—physically with powerful contractions and chemically with the action of enzymes,” says Jon Cucura, R.D., a dietitian with the FirstHealth Center for Health & Fitness-Richmond.

First, the stomach acts as a kind of holding tank by storing the swallowed food and liquid. Second, the stomach mixes up the food, liquid and the digestive juices. The digestive glands in the stomach lining produce hydrochloric acid and an enzyme that digests protein. The muscle in the lower part of the stomach causes the churning action.

“The stomach’s churning ability takes the chewed food and basically makes it into a thick liquid material,” Dr. Varanasi says.

The third responsibility of the stomach is to empty the thick liquid slowly into the small intestine.
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