What Is the Digestive System?

Your Body Gets Nourishment and Energy Through the Digestive System

Digestive System
The digestive tract begins at the mouth and ends at the anus. Image © Stocktrek Images / Stocktrek Images / Getty Images

The digestive system is the group of organs that break down food in order to absorb its nutrients. The nutrients in food are used by the body as fuel to keep all the body systems working. The leftover parts of food which cannot be broken down, digested, or absorbed are excreted as bowel movements (stool).

What Organs Are Part of the Digestive System?

There are several organs that are part of the digestive system.

Every organ has a role in breaking down food and managing the waste material. The digestive tract forms one long tube through the body, all the way from the mouth to the anus (with some sphincters between organs to keep things moving in the right direction). The organs in the digestive system, in the order in which food travels through them, are:

  • Mouth. Digestion starts at the very beginning, with food being chewed in the mouth. Food is broken down into smaller pieces and the saliva in the mouth begins digesting it. An enzyme in saliva called amylase breaks certain starches down into the smaller sugars, maltose and dextrin.
  • Esophagus. The esophagus is a tube that's inside the throat, behind the windpipe. After food is chewed and swallowed, it travels down through the esophagus and to the stomach. The muscles in the esophagus contract to move food along, which is called peristalsis.
  • Stomach. After the food is deposited in the stomach, the digestive process continues. The food is mixed with the acids and enzymes that are secreted from the stomach wall. After the food is thoroughly broken down, it is moved along into the small intestine.  
  • Small Intestine. The small intestine is a long tube where most of the vitamins and nutrients are absorbed from food into the bloodstream. More enzymes are added into the small intestine as the food moves through to help facilitate the process. The small intestine is composed of three parts, the duodenum, the jejunum, and the ileum.
  • Large Intestine. After moving through the small intestine, the food is now partially digested and mostly in a liquid form as it passes through a sphincter called the ileocecal valve and enters the large intestine. The large intestine is where much of the water is absorbed from the waste material. By the time the stool reaches the end of the large intestine it is in a more solid form. The sections of the large intestine are called the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon.
  • Rectum. At the end of the large intestine is the rectum, a reservoir that holds stool until it can be passed out of the body. When the rectum becomes full with stool, it gives off a signal to the brain that it's time to go to the bathroom.
  • Anus. The anus has two sphincters that serve to hold stool inside the body until it is time to pass it. When a person consciously relaxes their external sphincter, the stool can then leave the body. 

Can You Live Without Parts of the Digestive System?

When the digestive system is affected by certain diseases, surgery may be used as a treatment. This is true in particular cases of cancer and in severe cases of inflammatory bowel disease (IBD). Some parts of the digestive tract can be removed in part or in full.

The large intestine can be removed partially or fully, and an ileostomy or a colostomy or a pelvic pouch may be created. Most people live full and productive lives after these surgeries. In some cases, the rectum and the anus may need to be removed, and an ostomy is created in this situation as well. Parts of the small intestine can be removed, but since this is where most nutrients are absorbed, an effort is made to keep as much of it intact as possible. Part of the stomach being removed is another surgery that might be done, and people can live well after this surgery as well.

How IBD May Affect the Digestive Tract

Crohn's disease can affect any of the organs in the digestive tract, though the small intestine and large intestine are the ones that are most often involved.

Ulcerative colitis, a second main form of IBD, primarily affects the large intestine. Both forms of IBD can also involve parts of the body outside the digestive tract.

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