The Digestive System: How It Works

The Digestive System: How It Works

The digestive system consists of parts of the body working together to change the food we eat and liquids we drink into the fuel and building blocks our bodies need. Digestion (i.e., the process of breaking down food) may take several hours or a few days, depending on what you eat. Each body part in the digestive system—mouth, esophagus, stomach, small intestine, pancreas, liver, gallbladder, large intestine, colon, and rectum—plays an important role in digestion.


The mouth starts the digestive process by producing saliva even before eating begins. Thinking about or seeing tasty food will trigger saliva to form, beginning the digestive process. As food enters the mouth, it is broken down into smaller pieces by your teeth, while the tongue aides in the mixing process.

Esophagus (Food Pipe)

The esophagus is a stretchy tube approximately 10” long in adults that moves food from the throat to the stomach. Muscular contractions in the walls of the esophagus continue the digestive process by slowly squeezing the food until it reaches the stomach, which takes about two to three seconds.

The esophagus is one of two tubes, or pipes, extending from the back of the throat. The second tube is the windpipe that allows air intake. At the top of the windpipe is a special flap called the epiglottis, which opens when you breathe and closes when food is swallowed to ensure that food goes into the esophagus, rather than the windpipe, as it travels to your stomach.


The stomach is a hollow, stretchy sack similar in shape to the letter J and is attached to the end of the esophagus. The stomach has three important tasks:

  1. Store food that has entered through the esophagus
  2. Break down stored food into a more liquid form
  3. Slowly empty the liquid mixture into the small intestine

Stomach muscles continue the digestive process by churning and mashing the food into a more usable form. Enzymes in the gastric juices secreted from glands in the stomach walls aid the breakdown process and help kill bacteria that may have been eaten. From here, the food is very liquid and ready to be released to the small intestine.

Small Intestine

The small intestine is a tightly packed tube in the abdomen below the stomach. It measures approximately 1½ to 2 inches around and, if stretched out, is about 20 feet long in adults. The top end connects to the stomach, and the bottom end connects to the large intestine. The lining of the small intestine is made of tiny, finger-shaped tissues called villi. These raised tissues increase the surface area of the small intestine where calories and nutrients from the food consumed will be digested and absorbed.

There are three parts that make up the small intestine:

  1. Duodenum—first part of the small intestine where the food mixture is combined with digestive enzymes from the pancreas to break down fats, proteins, and carbohydrates, while bile from the liver or gallbladder helps absorb fats
  2. Jejunum—middle section which is responsible for the absorption of nutrients into the blood stream
  3. Ileum—third section which is attached to the large intestine and also responsible for absorption of nutrients into the bloodstream

Food may spend as long as four hours in the small intestine. After the nutrients are absorbed, the leftover food residue is passed into the large intestine.

Large Intestine

The large intestine would measure approximately five feet long if spread out. It is a highly specialized organ where water is eliminated and waste is processed so it can be eliminated easily through the rectum. There are three main parts:

  1. Cecum—attached to this is a tiny tube with a closed end, called the appendix
  2. Colon—this is where the body gets its last chance to absorb water and minerals into the bloodstream; as the water leaves the waste product in the colon, what’s left gets harder and harder as it keeps moving along, until it becomes a solid that the colon pushes into the rectum
  3. Rectum—this is the small tube attached to the end of the large intestine where you hold solid waste until you’re ready to go to the bathroom

Help your digestive system stay healthy by drinking lots of water and eating a healthy diet. Eating foods rich in fiber, and plenty of fruits, vegetables, and whole grains will help your body grow properly and stay healthy. Getting regular exercise also helps your digestive system move and operate at its best.

If you would like more information about gastrointestinal (GI) digestive disorders and nutrition in children, please contact Dr. Mona Dave’s Frisco Office or Request Appointment Here.