Digestive System -- An OverviewDigestive System -- An Overview

The Digestive System: An Overview

What is digestion?

Food and drink must be changed into smaller molecules of nutrients to be absorbed into the blood and carried to cells throughout the body. Digestion is the process by which food and liquid are broken down into smaller parts. The body can then use them to build and nourish cells and to make energy.

How does the digestive process work?

Digestion involves:

  • The mixing of food

  • The movement of food through the digestive tract

  • A chemical breakdown of large molecules of food into smaller molecules

Digestion begins in the mouth, where food and liquids are taken in. It is completed in the small intestine.

What is included in the digestive system?



  • Mouth

  • Esophagus

  • Stomach

  • Small intestine

  • Large intestine (includes the colon and rectum)

  • Anus

Organs that help with digestion, but are not part of the digestive tract, are the:

  • Tongue

  • Glands in the mouth that make saliva

  • Pancreas

  • Liver

  • Gallbladder


How does food move through the digestive system?

Muscles propel food and liquid along the digestive tract in a wave-like movement. This movement is called peristalsis. In general, there are 6 steps in the process of moving food and liquid through the digestive system:

  1. The first step in the digestive process occurs in the mouth. This is where food is chewed and broken down into a size that can be safely swallowed. The start of swallowing food or liquid is voluntary. But once it begins, the process becomes involuntary and continues under the control of the nerves.



  4. The food then enters the stomach. The stomach completes 3 mechanical tasks. It stores, mixes, and empties:


    • Second, the lower part of the stomach mixes up the food, liquid, and digestive juices made by the stomach through muscle action.


  5. The food is digested in the small intestine. It is dissolved by the juices from the pancreas, liver, and intestine. The contents of the intestine are mixed and pushed forward to allow further digestion.

  6. Last, the digested nutrients are absorbed through the intestinal walls. The waste products, including undigested parts of the food (fiber) and older cells that have been shed from the lining of the intestine (mucosa), move into the colon. Waste products in the colon often remain for a day or two until the feces are expelled by a bowel movement.

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