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The Digestive System

Food's Journey Through the Digestive System continued...

The rectum is an eight-inch chamber that connects the colon to the anus. The rectum:

  • Receives stool from the colon
  • Lets the person know there is stool to be evacuated
  • Holds the stool until evacuation happens

When anything (gas or stool) comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters relax and the rectum contracts, expelling its contents. If the contents cannot be expelled, the sphincters contract and the rectum accommodates so that the sensation temporarily goes away.

The anus is the last part of the digestive tract. It consists of the muscles that line the pelvis (pelvic floor muscles) and two other muscles called anal sphincters (internal and external).

The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The anal sphincters provide fine control of stool. The internal sphincter is always tight, except when stool enters the rectum. It keeps us continent (not releasing stool) when we are asleep or otherwise unaware of the presence of stool. When we get an urge to defecate (go to the bathroom), we rely on our external sphincter to keep the stool in until we can get to the toilet.

Accessory Digestive Organs

Among other functions, the pancreas is the chief factory for digestive enzymes that are secreted into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates.

The liver has multiple functions, but two of its main functions within the digestive system are to make and secrete an important substance called bile and to process the blood coming from the small intestine containing the nutrients just absorbed. The liver purifies this blood of many impurities before traveling to the rest of the body.

The gallbladder is a storage sac for excess bile. Bile made in the liver travels to the small intestine via the bile ducts. If the intestine doesn't need it, the bile travels into the gallbladder, where it awaits the signal from the intestines that food is present. Bile serves two main purposes. First, it helps absorb fats in the diet, and secondly, it carries waste from the liver that cannot go through the kidneys.

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WebMD Medical Reference

Reviewed by Kimball Johnson, MD on July 25, 2012

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